encryption.filekeys_emptyfile fails in buildbot with valgrind

encryption.filekeys_emptyfile 'xtradb'   w2 [ fail ]  Found warnings/errors in server log file!

        Test ended at 2016-09-25 07:31:56

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==1964== Conditional jump or move depends on uninitialised value(s)

==1964==    at 0xFFDC75: is_prefix (is_prefix.c:42)

==1964==    by 0xB5ED8EF: Parser::read_and_decrypt_file(char const*) (parser.cc:336)

==1964==    by 0xB5EDA76: Parser::parse_file(Dynamic_array<keyentry>*, char const*) (parser.cc:196)

==1964==    by 0xB5EDC0C: Parser::parse(Dynamic_array<keyentry>*) (parser.cc:159)

==1964==    by 0xB5ECDC7: file_key_management_plugin_init(void*) (file_key_management_plugin.cc:169)

==1964==    by 0x85A3BE: initialize_encryption_plugin(st_plugin_int*) (encryption.cc:53)

==1964==    by 0x6A84D8: plugin_initialize(st_mem_root*, st_plugin_int*, int*, char**, bool) (sql_plugin.cc:1408)

==1964==    by 0x6ACCD9: plugin_init(int*, char**, int) (sql_plugin.cc:1685)

==1964==    by 0x5CB825: init_server_components() (mysqld.cc:5188)

==1964==    by 0x5CD8CC: mysqld_main(int, char**) (mysqld.cc:5768)

==1964==    by 0x5BCE16: main (main.cc:25)