Bug 1426056. P4 - fix a case where we don't reopen the channel. r=bechen,gerald

In MediaCacheStream::NotifyResume(), it will not reopen the channel if
|mChannelOffset==mStreamLength && 0 <= mSeekTarget < mStreamLength| while we should.

MozReview-Commit-ID: 2knkgy6FEVw

--HG--
extra : rebase_source : 28e7910572bd25d189b942f9961f77ec336dea19

dom/media/MediaCache.cpp

@@ -2314,8 +2314,8 @@ MediaCacheStream::NotifyResume()
       }
       // Don't resume download if we are already at the end of the stream for
       // seek will fail and be wasted anyway.
-      if (mStreamLength < 0 || mChannelOffset < mStreamLength) {
-        int64_t offset = mSeekTarget != -1 ? mSeekTarget : mChannelOffset;
+      int64_t offset = mSeekTarget != -1 ? mSeekTarget : mChannelOffset;
+      if (mStreamLength < 0 || offset < mStreamLength) {
         mClient->CacheClientSeek(offset, false);
         // DownloadResumed() will be notified when a new channel is opened.
       }