wined3d: Make sure we release the correct DC in context_update_window().

dlls/wined3d/context.c

@@ -873,7 +873,18 @@ static void context_update_window(struct wined3d_context *context)
 
     if (context->valid)
     {
-        if (!ReleaseDC(context->win_handle, context->hdc))
+        /* You'd figure ReleaseDC() would fail if the DC doesn't match the
+         * window. However, that's not what actually happens, and there are
+         * user32 tests that confirm ReleaseDC() with the wrong window is
+         * supposed to succeed. So explicitly check that the DC belongs to
+         * the window, since we want to avoid releasing a DC that belongs to
+         * some other window if the original window was already destroyed. */
+        if (WindowFromDC(context->hdc) != context->win_handle)
+        {
+            WARN("DC %p does not belong to window %p.\n",
+                    context->hdc, context->win_handle);
+        }
+        else if (!ReleaseDC(context->win_handle, context->hdc))
         {
             ERR("Failed to release device context %p, last error %#x.\n",
                     context->hdc, GetLastError());