BVHTreeNearest index wasnt reset to -1.
If we have previously found something [making nearest.index non-zero],
and then for the next vertex dont find anything, we still have a non-zero
index leading to false positives in the following code.
Note that it might very well possible to reset 'nearest->index' to -1 in
'BLI_bvhtree_find_nearest_ex' even (since most code I've checked does
this prior to calling anyways) but being close to RC it might be better
to play safe for now...