CoreDump using set env MARIADB_PLUGIN_DIR

When setting env MARIADB_PLUGIN_DIR, call mysql_init(NULL) will coredup. The mysql->net.extension is null.
The backtrace as follow:

(gdb) bt
#0 0x000000000041f33d in mysql_load_plugin_v (mysql=0x7ffcce1e3650,
name=0x18b2cb0 "/public1/home/wugh/usr/lib64/mysql/plugin/", type=-1, argc=0, args=args@entry=0x7ffcce1e3558)
at /home/wugh/tools/mariadb-10.4.12/mybuild/libmariadb/libmariadb/ma_client_plugin.c:377
#1 0x000000000041f5ea in mysql_load_plugin (mysql=mysql@entry=0x7ffcce1e3650,
name=name@entry=0x18b2cb0 "/public1/home/wugh/usr/lib64/mysql/plugin/", type=type@entry=-1, argc=argc@entry=0)
at /home/wugh/tools/mariadb-10.4.12/mybuild/libmariadb/libmariadb/ma_client_plugin.c:479
#2 0x000000000041f7a9 in load_env_plugins (mysql=0x7ffcce1e3650)
at /home/wugh/tools/mariadb-10.4.12/mybuild/libmariadb/libmariadb/ma_client_plugin.c:254
#3 mysql_client_plugin_init ()
at /home/wugh/tools/mariadb-10.4.12/mybuild/libmariadb/libmariadb/ma_client_plugin.c:297
#4 0x000000000040df6a in mysql_once_init ()
at /home/wugh/tools/mariadb-10.4.12/libmariadb/libmariadb/mariadb_lib.c:3564
#5 0x00002b22fd57020b in __pthread_once_slow () from /lib64/libpthread.so.0
#6 0x000000000040dd53 in mysql_server_init (argc=argc@entry=0, argv=argv@entry=0x0, groups=groups@entry=0x0)
at /home/wugh/tools/mariadb-10.4.12/libmariadb/libmariadb/mariadb_lib.c:3629
#7 0x000000000040dd75 in mysql_init (mysql=0x0)
at /home/wugh/tools/mariadb-10.4.12/libmariadb/libmariadb/mariadb_lib.c:996

(gdb) p mysql->net.extension
$6 = (struct st_mariadb_net_extension *) 0x0