vulkan/wsi/x11: don't crash on null wsi x11 connection

Without this check driver crash when application window
closed unexpectedly.

Acked-by: Edward O'Callaghan <funfunctor@folklore194.net>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Cc: "13.0" <mesa-stable@lists.freedesktop.org>

src/vulkan/wsi/wsi_common_x11.c

@@ -261,6 +261,9 @@ VkBool32 wsi_get_physical_device_xcb_presentation_support(
    struct wsi_x11_connection *wsi_conn =
       wsi_x11_get_connection(wsi_device, alloc, connection);
 
+   if (!wsi_conn)
+      return false;
+
    if (!wsi_conn->has_dri3) {
       fprintf(stderr, "vulkan: No DRI3 support\n");
       return false;