Bug 1297880: Have GetSeekable return an empty range if duration is not r=jwwang

yet known. r?jwwang

MozReview-Commit-ID: 4e1k42FlW1z

--HG--
extra : rebase_source : 47c94026157a278192f2388a4d92768d5454c384

dom/media/MediaDecoder.cpp

@@ -1425,6 +1425,12 @@ media::TimeIntervals
 MediaDecoder::GetSeekable()
 {
   MOZ_ASSERT(NS_IsMainThread());
+
+  if (IsNaN(GetDuration())) {
+    // We do not have a duration yet, we can't determine the seekable range.
+    return TimeIntervals();
+  }
+
   // We can seek in buffered range if the media is seekable. Also, we can seek
   // in unbuffered ranges if the transport level is seekable (local file or the
   // server supports range requests, etc.) or in cue-less WebMs