The search routine begins searching right after the cursor and behaves
as if the line starts there, which means that a beginning-of-word anchor
(\< or \b) will match there also when in fact the cursor is sitting in
the middle of a word.  To prevent finding a false match, verify that
for a regex that starts with a BOW anchor the found match is actually
the start of a word.

This fixes https://savannah.gnu.org/bugs/?45630.