fix handling of flags in the OSC input handler

Some builds of glib on macOS end up delivering IO_PRI when IO_IN is also set. This differs from our own build stack
version, but it isn't really an error, so we should handle it.

libs/surfaces/osc/osc.cc

@@ -684,14 +684,14 @@ OSC::register_callbacks()
 bool
 OSC::osc_input_handler (IOCondition ioc, lo_server srv)
 {
-	if (ioc & ~IO_IN) {
-		return false;
-	}
-
 	if (ioc & IO_IN) {
 		lo_server_recv (srv);
 	}
 
+	if (ioc & ~(IO_IN|IO_PRI)) {
+		return false;
+	}
+
 	return true;
 }