Emit xwayland unmap signal before unmapping

This allows compositors to access the surface being unmapped. This
is also more consistent with the destroy signal.

xwayland/xwm.c

@@ -743,6 +743,11 @@ static void xwm_handle_unmap_notify(struct wlr_xwm *xwm,
 		return;
 	}
 
+	if (xsurface->mapped) {
+		xsurface->mapped = false;
+		wlr_signal_emit_safe(&xsurface->events.unmap, xsurface);
+	}
+
 	if (xsurface->surface_id) {
 		// Make sure we're not on the unpaired surface list or we
 		// could be assigned a surface during surface creation that
@@ -757,11 +762,6 @@ static void xwm_handle_unmap_notify(struct wlr_xwm *xwm,
 	}
 	xsurface->surface = NULL;
 
-	if (xsurface->mapped) {
-		xsurface->mapped = false;
-		wlr_signal_emit_safe(&xsurface->events.unmap, xsurface);
-	}
-
 	xsurface_set_wm_state(xsurface, ICCCM_WITHDRAWN_STATE);
 }