Bug 1138557 - Add null check to mLoadingSrc. r=karlt

--HG--
extra : rebase_source : 521a2570029605e7c9e5388feb627ef3a30841a7

dom/html/HTMLMediaElement.cpp

@@ -3295,7 +3295,7 @@ void HTMLMediaElement::CheckProgress(bool aHaveNewProgress)
   if (now - mDataTime >= TimeDuration::FromMilliseconds(STALL_MS)) {
     DispatchAsyncEvent(NS_LITERAL_STRING("stalled"));
 
-    if (IsMediaSourceURI(mLoadingSrc)) {
+    if (mLoadingSrc && IsMediaSourceURI(mLoadingSrc)) {
       ChangeDelayLoadStatus(false);
     }