MDEV-24901 SIGSEGV in fts_get_table_name, SIGSEGV in ib_vector_size, SIGSEGV in row_merge_fts_doc_tokenize, stack smashing

strmake() puts one extra 0x00 byte at the end of the string.
The code in my_strnxfrm_tis620[_nopad] did not take this into
account, so in the reported scenario the 0x00 byte was put outside
of a stack variable, which made ASAN crash.

This problem is already fixed in in MySQL:

  commit 19bd66fe43c41f0bde5f36bc6b455a46693069fb
  Author: bin.x.su@oracle.com <>
  Date:   Fri Apr 4 11:35:27 2014 +0800

But the fix does not seem to be correct, as it breaks when finds a zero byte
in the source string.

Using memcpy() instead of strmake().

- Unlike strmake(), memcpy() it does not write beyond the destination
  size passed.
- Unlike the MySQL fix, memcpy() does not break on the first 0x00 byte found
  in the source string.