import from UXP: Fix cache v1 compression crash in nsCompressOutputStreamWrapper::Close() (8c917ef3)

netwerk/cache/nsCacheEntryDescriptor.cpp

@@ -1399,6 +1399,12 @@ nsCompressOutputStreamWrapper::Close()
     // Do not allow to initialize stream after calling Close().
     mStreamEnded = true;
 
+    // In some rare cases, flushing the zlib stream can take too long
+    // and we lose our cache entry in the meantime. Do another check
+    // and bail if so.
+    if (!mDescriptor)
+        return NS_ERROR_NOT_AVAILABLE;
+
     if (mDescriptor->CacheEntry()) {
         nsAutoCString uncompressedLenStr;
         rv = mDescriptor->GetMetaDataElement("uncompressed-len",