Bug 1482640 - Null out mDecoder in OnStopRequest to avoid asserting when there is more than one OnStopRequest. r=smaug

MozReview-Commit-ID: K25XhiYGzhl

Differential Revision: https://phabricator.services.mozilla.com/D3217

--HG--
extra : moz-landing-system : lando

dom/xhr/XMLHttpRequestMainThread.cpp

@@ -2088,6 +2088,8 @@ XMLHttpRequestMainThread::OnStopRequest(nsIRequest *request, nsISupports *ctxt,
   // but only when parsing text (not XML, which does this already).
   if (mDecoder && !mFlagParseBody) {
     AppendToResponseText(nullptr, 0, true);
+    // Null out the decoder to ignore subsequent OnStopRequest calls
+    mDecoder = nullptr;
   }
 
   mWaitingForOnStopRequest = false;