fix bad shift in conditional netmask ".../0" handling

config conditionals like $HTTP["remoteip"] == "a.b.c.d/0" (or completely
broken netmasks) triggered bad shifts. Matching against "/0" is not very
useful though - it is always true.

From: Stefan Bühler <stbuehler@web.de>

git-svn-id: svn://svn.lighttpd.net/lighttpd/branches/lighttpd-1.4.x@2963 152afb58-edef-0310-8abb-c4023f1b3aa9