core: Fix root configure event being ignored

The guard added in commit 0aa620 to avoid duplicates filters out all Configure events on the root window, causing picom
to not properly render the screen area after display configuration changes, such as adding or resizing a monitor.

Only apply the guard if the Configure event affects a window other than the root window.

Fixes #1338

src/event.c

@@ -388,13 +388,13 @@ static inline void ev_configure_notify(session_t *ps, xcb_configure_notify_event
 		return;
 	}
 
-	if (ev->window == ev->event) {
-		return;
-	}
-
 	if (ev->window == ps->c.screen_info->root) {
 		configure_root(ps);
 	} else {
+		if (ev->window == ev->event) {
+			return;
+		}
+
 		configure_win(ps, ev);
 	}
 }