user32: Fix NULL dereference in UnregisterDeviceNotification.

dlls/sechost/service.c

@@ -2109,6 +2109,9 @@ BOOL WINAPI I_ScUnregisterDeviceNotification( HDEVNOTIFY handle )
 
     TRACE("%p\n", handle);
 
+    if (!handle)
+        return FALSE;
+
     EnterCriticalSection( &service_cs );
     list_remove( &registration->entry );
     LeaveCriticalSection(&service_cs);

dlls/user32/tests/input.c

@@ -3004,6 +3004,12 @@ static void test_GetPointerType(void)
     ok(type == PT_MOUSE, " type %d\n", type );
 }
 
+static void test_UnregisterDeviceNotification(void)
+{
+    BOOL ret = UnregisterDeviceNotification(NULL);
+    ok(ret == FALSE, "Unregistering NULL Device Notification returned: %d\n", ret);
+}
+
 START_TEST(input)
 {
     POINT pos;
@@ -3050,4 +3056,6 @@ START_TEST(input)
         test_GetPointerType();
     else
         win_skip("GetPointerType is not available\n");
+
+    test_UnregisterDeviceNotification();
 }