The patch fixes the problem with loading information from system tables
(e.g. event and help related tables) when PAD_CHAR_TO_FULL_LENGTH is enabled,
as well as includes some additional minor improvements:
- refactoring in get_field() to return an error rather than success
  if strmake_root() failed
- removing of duplicate code in similar functions:
  char *get_field(MEM_ROOT *mem, Field *field)
  bool get_field(MEM_ROOT *mem, Field *field, String *res)