regcomp.c: add missing code for optimizer for \W

regcomp.c: add missing code for optimizer for \W

The code here was asymmetrical.  It did not account for Unicode
semantics when ORing \W.  For \w, \s, and \S it does.  This patch
changes the code to be symmetrical.

I spent a couple hours trying to come up with a test, but could not get
this area of the code to execute, which may explain why there has not
been a field report of it.  It may be that it is unreachable; there has
been other code in the routine that wasn't.