Fix expanding 'bounds' in pg_trgm's calc_word_similarity() function

Fix expanding 'bounds' in pg_trgm's calc_word_similarity() function

If the 'bounds' array needs to be expanded, because the input contains
more trigrams than the initial guess, the code didn't return the
reallocated array correctly to the caller. That could lead to a crash
in the rare case that the input string becomes longer when it's
lower-cased. The only known instance of that is when an ICU locale is
used with certain single-byte encodings. This was an oversight in
commit 00896ddaf41f.

Author: Zsolt Parragi <zsolt.parragi@percona.com>
Backpatch-through: 18