parse: fix logical expression testing for non RFC1459 links

parse.c:284: warning: suggest parentheses around operand of '!' or
change '&' to '&&' or '!' to '~'

The expression looks dubious, this should probably be
an if-not-set, then... test.

src/ngircd/parse.c

@@ -280,7 +280,7 @@ Validate_Prefix( CONN_ID Idx, REQUEST *Req, bool *Closed )
 	assert( client != NULL );
 
 	if (!Req->prefix && Client_Type(client) == CLIENT_SERVER
-	    && !Conn_Options(Idx) & CONN_RFC1459
+	    && !(Conn_Options(Idx) & CONN_RFC1459)
 	    && strcasecmp(Req->command, "ERROR") != 0
 	    && strcasecmp(Req->command, "PING") != 0)
 	{