Bug 1806362 - FileQuotaStreamWithWrite::Write should return zero written bytes in the failure case; r=dom-storage-reviewers,jari

This bug causes NS_AsyncCopy to call the progress callback with random values
when there's an error during writing.

Depends on D165069

Differential Revision: https://phabricator.services.mozilla.com/D165070

dom/quota/FileStreams.cpp

@@ -93,6 +93,7 @@ NS_IMETHODIMP FileQuotaStreamWithWrite<FileStreamBase>::Write(
     if (!FileQuotaStreamWithWrite::mQuotaObject->MaybeUpdateSize(
             offset + int64_t(aCount),
             /* aTruncate */ false)) {
+      *_retval = 0;
       return NS_ERROR_FILE_NO_DEVICE_SPACE;
     }
   }