Bug 1312886: P2. Never move past HAVE_FUTURE_DATA if we're waiting for a key, r=cpearce

MozReview-Commit-ID: KWERB7zWXPZ

dom/html/HTMLMediaElement.cpp

@@ -4796,7 +4796,7 @@ HTMLMediaElement::UpdateReadyStateInternal()
   // autoplay elements for live streams will never play. Otherwise we
   // move to HAVE_ENOUGH_DATA if we can play through the entire media
   // without stopping to buffer.
-  if (mDecoder->CanPlayThrough()) {
+  if (mWaitingForKey == NOT_WAITING_FOR_KEY && mDecoder->CanPlayThrough()) {
     LOG(LogLevel::Debug, ("MediaElement %p UpdateReadyStateInternal() "
                           "Decoder can play through", this));
     ChangeReadyState(nsIDOMHTMLMediaElement::HAVE_ENOUGH_DATA);