Regexp_processor_pcre::fix_owner() called Regexp_processor_pcre::compile(),
which could fail on the regex syntax error in the pattern and put
an error into the diagnostics area. However, the callers:
  - Item_func_regex::fix_length_and_dec()
  - Item_func_regexp_instr::fix_length_and_dec()
still returned "false" in such cases, which made the code
crash later inside Diagnostics_area::set_ok_status().

Fix:

- Change the return type of fix_onwer() from "void" to "bool"
  and return "true" whenever an error is put to the DA
  (e.g. on the syntax error in the pattern).
- Fixing fix_length_and_dec() of the mentioned Item_func_xxx
  classes to return "true" if fix_onwer() returned "true".