Assume that tablet is always valid in ForwardInputFilter

Previously, there used be issues with unregistration of tablet input
devices, which are resolved now. So, the null checks can be dropped to
make the code easier.

src/input.cpp

@@ -2038,22 +2038,19 @@ public:
             return false;
         }
 
-        TabletToolV2Interface *tool = input()->tablet()->ensureTabletTool(event->toolId());
-
-        // NOTE: tablet will be nullptr as the device is removed (see ::removeDevice) but events from the tool
-        // may still happen (e.g. Release or ProximityOut events)
-        TabletSeatV2Interface *seat = waylandServer()->tabletManagerV2()->seat(waylandServer()->seat());
-        auto tablet = seat->tabletByName(event->device()->sysName());
-
         Window *window = input()->findToplevel(event->globalPosF());
         if (!window || !window->surface()) {
             return false;
         }
 
+        TabletSeatV2Interface *seat = waylandServer()->tabletManagerV2()->seat(waylandServer()->seat());
+        TabletToolV2Interface *tool = input()->tablet()->ensureTabletTool(event->toolId());
+        TabletV2Interface *tablet = seat->tabletByName(event->device()->sysName());
+
         SurfaceInterface *surface = window->surface();
         tool->setCurrentSurface(surface);
 
-        if (!tool->isClientSupported() || (tablet && !tablet->isSurfaceSupported(surface))) {
+        if (!tool->isClientSupported() || !tablet->isSurfaceSupported(surface)) {
             return emulateTabletEvent(event);
         }