Bug 1356854 - Check mFD is not null before PR_Write r=mcmanus

MozReview-Commit-ID: INoTUvPpPrs

--HG--
extra : rebase_source : bb8f25d66c2f5fbaec2f344b69bb42c0ef38b7d2

netwerk/base/nsFileStreams.cpp

@@ -378,6 +378,9 @@ nsFileStreamBase::DoPendingOpen()
 
     case eOpened:
         MOZ_ASSERT(mFD);
+        if (NS_WARN_IF(!mFD)) {
+          return NS_ERROR_FAILURE;
+        }
         return NS_OK;
 
     case eClosed: