irc.c: Fix handling of channels containing dots

irc.c: Fix handling of channels containing dots

commit 2546a13ad2949192eb70bf21e114ec60af287ee4
('Cumulative Message Patch') broke PRIVMSG to channels
containing dots.

Fix this by switching evaluation order:
Check first if the target matches a existing channel and only do a check
for target masks if that failed.

PRIVMSG with host/server masks is described in RFC 2812, section 3.3.1.

Makes one wonder how a server is _really_ supposed to tell the difference
between hostmasks and channel names.

Sigh.