GdkWin32: Fix warning due to changed device count

gdk/win32/gdkdevicemanager-win32.c

@@ -498,17 +498,30 @@ winpointer_enumerate_devices (GdkDeviceManagerWin32 *device_manager)
   UINT32 i = 0;
   GList *current = NULL;
 
-  do
+  if (!getPointerDevices (&infos_count, NULL))
     {
+      WIN32_API_FAILED ("GetPointerDevices");
+      return;
+    }
+
   infos = g_new0 (POINTER_DEVICE_INFO, infos_count);
+
+  /* Note: the device count may increase between the two
+   * calls. In such case, the second call will fail with
+   * ERROR_INSUFFICIENT_BUFFER.
+   * However we'll also get a new WM_POINTERDEVICECHANGE
+   * notification, which will start the enumeration again.
+   * So do not treat ERROR_INSUFFICIENT_BUFFER as an
+   * error, rather return and do the necessary work later
+   */
+
   if (!getPointerDevices (&infos_count, infos))
     {
+      if (GetLastError() != ERROR_INSUFFICIENT_BUFFER)
         WIN32_API_FAILED ("GetPointerDevices");
       g_free (infos);
       return;
     }
-    }
-  while (infos_count > 0 && !infos);
 
   /* remove any gdk device not present anymore or update info */
   current = device_manager->winpointer_devices;