IrcNetwork: initialize modes, prefixes & channel types

So that such "IRC" networks as Twitch that don't send RPL_ISUPPORT
still get sensible behavior for IrcBufferModel and IrcUserModel, that
is, channels treated as channels.

src/core/ircnetwork.cpp

@@ -182,7 +182,7 @@ IRC_BEGIN_NAMESPACE
  */
 
 #ifndef IRC_DOXYGEN
-IrcNetworkPrivate::IrcNetworkPrivate() : q_ptr(0), initialized(false)
+IrcNetworkPrivate::IrcNetworkPrivate() : q_ptr(0), initialized(false), modes("ov"), prefixes("@+"), channelTypes("#")
 {
 }