wayland: call W_CheckTimerHandlers in event loop for workspace fade

WINGs timers (used by workspace name fade animation) were never firing
because the compositor event loop never called W_CheckTimerHandlers.
This function is normally invoked by WMNextEvent, but the compositor
uses a custom loop. Add the call so timers fire each iteration.

src/backend/wayland/wl_backend.c

@@ -3695,6 +3695,9 @@ wl_event_loop_run(void)
             }
 #endif
 
+            /* Fire any expired WINGs timers (workspace name fade, etc.) */
+            W_CheckTimerHandlers();
+
             /* Drain WINGs event queue */
             WMScreen *wmscr = wl_get_wmscreen();
             if (wmscr) {