Use Scintilla's definition of a "word" when fetching the current word
to perform a search.  This is needed when we perform a whole-word
search for Scintilla to find the matches.

Closes #3386129.

git-svn-id: https://geany.svn.sourceforge.net/svnroot/geany/trunk@5895 ea778897-0a13-0410-b9d1-a72fbfd435f5