patch 9.2.0476: pattern completion leaks memory on alloc failures

patch 9.2.0476: pattern completion leaks memory on alloc failures

Problem:  copy_substring_from_pos() leaked on ga_grow() failures,
          expand_pattern_in_buf() leaked "match" on ga_grow() failure,
          fuzzy_match_str_with_pos() ignored ga_grow() failures
Solution: Route failures through cleanup paths, check ga_grow before
          writing to ga_data (glepnir)

closes: #20203

Signed-off-by: glepnir <glephunter@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>