[gnome-software] GsApp: Add missing locking to gs_app_add_screenshot()

[Kalev Lember <klember src gnome org>]

commit ec358a4897fa2d3b06495a73d1813e68d733d804
Author: Kalev Lember <klember redhat com>
Date:   Wed Nov 7 14:40:52 2018 +0100

    GsApp: Add missing locking to gs_app_add_screenshot()
    
    https://bugzilla.redhat.com/show_bug.cgi?id=1646540

 lib/gs-app.c | 4 ++++
 1 file changed, 4 insertions(+)
---
diff --git a/lib/gs-app.c b/lib/gs-app.c
index 5dd12bf9..77b3862b 100644
--- a/lib/gs-app.c
+++ b/lib/gs-app.c
@@ -2614,8 +2614,12 @@ void
 gs_app_add_screenshot (GsApp *app, AsScreenshot *screenshot)
 {
        GsAppPrivate *priv = gs_app_get_instance_private (app);
+       g_autoptr(GMutexLocker) locker = NULL;
+
        g_return_if_fail (GS_IS_APP (app));
        g_return_if_fail (AS_IS_SCREENSHOT (screenshot));
+
+       locker = g_mutex_locker_new (&priv->mutex);
        g_ptr_array_add (priv->screenshots, g_object_ref (screenshot));
 }