USAN: checking identifier names for 0 length names

$ cat /tmp/t.sql

CREATE DATABASE test;

CREATE TABLE test.t (i int not null primary key);

$ gdb -ex  'b __asan_report_error' -ex 'b __ubsan::ScopedReport::~ScopedReport'  sql/mariadbd

(gdb) r --no-defaults --skip-networking --datadir=$(mktemp -d) --bootstrap < /tmp/t.sql

#0  0x00000000005a4dc0 in __ubsan::ScopedReport::~ScopedReport() ()

#1  0x00000000005a928e in handleNonNullArg(__ubsan::NonNullArgData*, __ubsan::ReportOptions, bool) ()

#2  0x00000000005a900d in __ubsan_handle_nonnull_arg ()

#3  0x000000000075fa72 in Well_formed_prefix_status::Well_formed_prefix_status (this=0x7ffff5594c20, cs=0x85b03c0 <my_charset_utf8mb3_general1400_as_ci>, str=0x0, end=0x0, nchars=64)

    at /home/dan/repos/mariadb-server-11.8/include/m_ctype.h:1949

#4  0x0000000000a02b54 in Well_formed_prefix::Well_formed_prefix (this=0x7ffff5594c20, cs=0x85b03c0 <my_charset_utf8mb3_general1400_as_ci>, str=0x0, length=0, nchars=64)

    at /home/dan/repos/mariadb-server-11.8/include/m_ctype.h:1963

#5  0x0000000000e6b908 in check_string_char_length (str=0x52d00033f010, err_msg=0, max_char_length=64, cs=0x85b03c0 <my_charset_utf8mb3_general1400_as_ci>, no_error=true)

    at /home/dan/repos/mariadb-server-11.8/sql/sql_parse.cc:10118

#6  0x0000000000e4ec8a in check_ident_length (ident=0x52d00033f010) at /home/dan/repos/mariadb-server-11.8/sql/sql_parse.cc:10136

#7  0x00000000013ef90d in mysql_prepare_create_table_finalize (thd=0x52b0000b6288, create_info=0x7ffff56ff070, alter_info=0x7ffff56ff370, db_options=0x7ffff5418e20, file=0x52d00033f388, 

    key_info_buffer=0x7ffff5593c20, key_count=0x7ffff5593c40, create_table_mode=0) at /home/dan/repos/mariadb-server-11.8/sql/sql_table.cc:3452

#8  0x00000000013ea090 in mysql_create_frm_image (thd=0x52b0000b6288, create_info=0x7ffff56ff070, alter_info=0x7ffff56ff370, create_table_mode=0, key_info=0x7ffff5593c20, 

    key_count=0x7ffff5593c40, frm=0x7ffff5593ee0) at /home/dan/repos/mariadb-server-11.8/sql/sql_table.cc:4544

#9  0x000000000140316f in create_table_impl (thd=0x52b0000b6288, ddl_log_state_create=0x7ffff5412620, ddl_log_state_rm=0x7ffff5412660, 

    orig_db=@0x52d00033e640: {<Lex_ident_fs> = {<Lex_ident<Compare_table_names>> = {<Lex_cstring> = {<st_mysql_const_lex_string> = {str = 0x52d00033e5c0 "test", length = 4}, <No data fields>}, <No data fields>}, <No data fields>}, <No data fields>}, 

    orig_table_name=@0x52d00033e650: {<Lex_ident_fs> = {<Lex_ident<Compare_table_names>> = {<Lex_cstring> = {<st_mysql_const_lex_string> = {str = 0x52d00033e5d8 "t", length = 1}, <No data fields>}, <No data fields>}, <No data fields>}, <No data fields>}, db=@0x52d00033e640: {str = 0x52d00033e5c0 "test", length = 4}, 

    table_name=@0x52d00033e650: {str = 0x52d00033e5d8 "t", length = 1}, path=@0x7ffff5593f00: {str = 0x7ffff5593c50 "./test/t", length = 8}, options={m_options = DDL_options_st::OPT_NONE}, 

    create_info=0x7ffff56ff070, alter_info=0x7ffff56ff370, create_table_mode=0, is_trans=0x7ffff54126a0, key_info=0x7ffff5593c20, key_count=0x7ffff5593c40, frm=0x7ffff5593ee0)

    at /home/dan/repos/mariadb-server-11.8/sql/sql_table.cc:4866

#10 0x00000000013fed9a in mysql_create_table_no_lock (thd=0x52b0000b6288, ddl_log_state_create=0x7ffff5412620, ddl_log_state_rm=0x7ffff5412660, create_info=0x7ffff56ff070, 

    alter_info=0x7ffff56ff370, is_trans=0x7ffff54126a0, create_table_mode=0, table_list=0x52d00033e628) at /home/dan/repos/mariadb-server-11.8/sql/sql_table.cc:4991

#11 0x000000000148d4c2 in mysql_create_table (thd=0x52b0000b6288, create_table=0x52d00033e628, create_info=0x7ffff56ff070, alter_info=0x7ffff56ff370)

    at /home/dan/repos/mariadb-server-11.8/sql/sql_table.cc:5233

#12 0x0000000001485707 in Sql_cmd_create_table_like::execute (this=0x52d00033e578, thd=0x52b0000b6288) at /home/dan/repos/mariadb-server-11.8/sql/sql_table.cc:13624

#13 0x0000000000e344af in mysql_execute_command (thd=0x52b0000b6288, is_called_from_prepared_stmt=false) at /home/dan/repos/mariadb-server-11.8/sql/sql_parse.cc:5886

#14 0x0000000000ddb081 in mysql_parse (thd=0x52b0000b6288, rawbuf=0x52d00033e4a8 "CREATE TABLE test.t (i int not null primary key);", length=49, parser_state=0x7ffff540c640)

    at /home/dan/repos/mariadb-server-11.8/sql/sql_parse.cc:7915

#15 0x0000000000dd9014 in bootstrap (file=0x9f3bde0 <instrumented_stdin>) at /home/dan/repos/mariadb-server-11.8/sql/sql_parse.cc:1090

#16 0x00000000005b63c1 in mysqld_main (argc=6, argv=0x521000000278) at /home/dan/repos/mariadb-server-11.8/sql/mysqld.cc:6091

#17 0x00000000005acb8a in main (argc=5, argv=0x7fffffffd388) at /home/dan/repos/mariadb-server-11.8/sql/main.cc:34

(gdb)  frame 7

#7  0x00000000013ef90d in mysql_prepare_create_table_finalize (thd=0x52b0000b6288, create_info=0x7ffff56ff070, alter_info=0x7ffff56ff370, db_options=0x7ffff5418e20, file=0x52d00033f388, 

    key_info_buffer=0x7ffff5593c20, key_count=0x7ffff5593c40, create_table_mode=0) at /home/dan/repos/mariadb-server-11.8/sql/sql_table.cc:3452

3452	    if (check_ident_length(&key->name))

(gdb) p key->name

$1 = {<Lex_ident_ci> = {<Lex_ident<Compare_ident_ci>> = {<Lex_cstring> = {<st_mysql_const_lex_string> = {str = 0x0, 

          length = 0}, <No data fields>}, <No data fields>}, <No data fields>}, <No data fields>}

diff --git a/sql/sql_table.cc b/sql/sql_table.cc

index ee1a0bb1c05..926cfff68ef 100644

--- a/sql/sql_table.cc

+++ b/sql/sql_table.cc

@@ -3449,7 +3449,7 @@ mysql_prepare_create_table_finalize(THD *thd, HA_CREATE_INFO *create_info,

       my_error(ER_TOO_MANY_KEY_PARTS,MYF(0),tmp);

       DBUG_RETURN(TRUE);

     }

-    if (check_ident_length(&key->name))

+    if (key->name.length && check_ident_length(&key->name))

       DBUG_RETURN(TRUE);

     key_iterator2.rewind ();

     if (key->type != Key::FOREIGN_KEY)