Fix packager failure if there is only one sample in a fragment

That is a very corner corner case.

Change-Id: I45bc6c2d41db2a666a4ad997e4bf2eb17843e3ea

media/formats/mp4/track_run_iterator.cc

@@ -446,7 +446,7 @@ int64 TrackRunIterator::GetMaxClearOffset() {
     }
   }
   if (offset == kint64max)
-    return 0;
+    return runs_.empty() ? 0 : runs_[0].sample_start_offset;
   return offset;
 }