test: Fix struct initialization warning

test/xtest.c

@@ -61,7 +61,7 @@ xtest_init_devices(void)
 {
     ScreenRec screen = {0};
     ClientRec server_client = {0};
-    WindowRec root = {0};
+    WindowRec root = {{0}};
     WindowOptRec optional = {0};
 
     /* random stuff that needs initialization */