Bug 1742975 - Ensure m_tempMessageStreamBytesWritten is initialized. r=freaktechnik

Differential Revision: https://phabricator.services.mozilla.com/D149597

--HG--
extra : rebase_source : 119b40cd2c5cb5c22f4b2a655f47c36aba8f48bc
extra : amend_source : 004a1c9d3585b28baca7d1ab4767f0b123a66431

mailnews/base/src/nsMsgDBFolder.cpp

@@ -229,6 +229,7 @@ nsMsgDBFolder::nsMsgDBFolder(void)
       mLastMessageLoaded(nsMsgKey_None),
       m_numOfflineMsgLines(0),
       m_bytesAddedToLocalMsg(0),
+      m_tempMessageStreamBytesWritten(0),
       mFlags(0),
       mNumUnreadMessages(-1),
       mNumTotalMessages(-1),