Avoid crashing when the video sink does not have stats

In the Sagemcom box without westeros, it crashes.

This was fixed upstream as commit that could not be backported because of the
differences with upstream. This one:

    commit 4f4db5a (HEAD -> main, origin/main, origin/HEAD)
    Author: Xabier Rodriguez-Calvar <calvaris@igalia.com>
    Date:   Thu Sep 19 22:40:41 2024 -0700

        [GStreamer] Do not access a null GstStructure
        https://bugs.webkit.org/show_bug.cgi?id=279972

        Reviewed by Philippe Normand.

        Stats can be null in some sinks so we avoid accessing them in that case. For the same prize we protect the access to
        null structures in the GstStructure accessors.

        * Source/WebCore/platform/graphics/gstreamer/GStreamerCommon.cpp:
        (WebCore::gstStructureGet):
        (WebCore::gstStructureGetString):
        (WebCore::gstStructureGetName):
        * Source/WebCore/platform/graphics/gstreamer/MediaPlayerPrivateGStreamer.cpp:
        (WebCore::MediaPlayerPrivateGStreamer::updateVideoSinkStatistics):

        Canonical link: https://commits.webkit.org/283974@main

Author: calvaris

Source/WebCore/platform/graphics/gstreamer/MediaPlayerPrivateGStreamer.cpp

@@ -4219,6 +4219,9 @@ bool MediaPlayerPrivateGStreamer::updateVideoSinkStatistics()
         GUniqueOutPtr<GstStructure> stats;
         g_object_get(m_videoSink.get(), "stats", &stats.outPtr(), nullptr);
 
+        if (!stats)
+            return false;
+
         if (!gst_structure_get_uint64(stats.get(), "rendered", &totalVideoFrames))
             return false;