Gracefully handle track-less elements on updating track selection.

Source/core/html/HTMLMediaElement.cpp

Index: Source/core/html/HTMLMediaElement.cpp
diff --git a/Source/core/html/HTMLMediaElement.cpp b/Source/core/html/HTMLMediaElement.cpp
index e905c8905d3cdb9f0a85e36d437d9eaacd134618..29a67a7b11065fab209b7ad7b989329a26b8ae6c 100644
--- a/Source/core/html/HTMLMediaElement.cpp
+++ b/Source/core/html/HTMLMediaElement.cpp
@@ -3287,7 +3287,8 @@ void HTMLMediaElement::automaticTrackSelectionForUpdatedUserPreference()
 
     // If a track is set to 'showing' post performing automatic track selection,
     // set closed captions state to visible to update the CC button and display the track.
-    m_closedCaptionsVisible = m_textTracks->hasShowingTracks();
+    if (m_textTracks)
+        m_closedCaptionsVisible = m_textTracks->hasShowingTracks();
     updateTextTrackDisplay();
 }