Cherry-pick 272910@main (2404f7b). https://bugs.webkit.org/show_bug.c…

…gi?id=267327

    [GStreamer][WebRTC] WPT test RTCPeerConnection-setLocalDescription-offer.html is crashing
    https://bugs.webkit.org/show_bug.cgi?id=267327

    Reviewed by Xabier Rodriguez-Calvar.

    Check the SDP message contains enough medias before attempting to access the one located at the
    given mline index.

    * Source/WebCore/Modules/mediastream/gstreamer/GStreamerMediaEndpoint.cpp:
    (WebCore::GStreamerMediaEndpoint::onIceCandidate):

    Canonical link: https://commits.webkit.org/272910@main

Source/WebCore/Modules/mediastream/gstreamer/GStreamerMediaEndpoint.cpp

@@ -1443,9 +1443,9 @@ void GStreamerMediaEndpoint::onIceCandidate(guint sdpMLineIndex, gchararray cand
         String mid;
         GUniqueOutPtr<GstWebRTCSessionDescription> description;
         g_object_get(m_webrtcBin.get(), "local-description", &description.outPtr(), nullptr);
-        if (description) {
-            if (const auto* media = gst_sdp_message_get_media(description->sdp, sdpMLineIndex))
-                mid = makeString(gst_sdp_media_get_attribute_val(media, "mid"));
+        if (description && sdpMLineIndex < gst_sdp_message_medias_len(description->sdp)) {
+            const auto media = gst_sdp_message_get_media(description->sdp, sdpMLineIndex);
+            mid = makeString(gst_sdp_media_get_attribute_val(media, "mid"));
         }
 
         auto descriptions = descriptionsFromWebRTCBin(m_webrtcBin.get());