fixed Mac build bustage

mailnews/imap/src/nsImapUndoTxn.cpp

@@ -20,6 +20,11 @@
 
 static NS_DEFINE_CID(kCImapService, NS_IMAPSERVICE_CID);
 
+nsImapMoveCopyMsgTxn::nsImapMoveCopyMsgTxn() :
+    m_srcMsgIdString("", eOneByte), m_dstMsgIdString("", eOneByte)
+{
+}
+
 nsImapMoveCopyMsgTxn::nsImapMoveCopyMsgTxn(
 	nsIMsgFolder* srcFolder, nsMsgKeyArray* srcKeyArray, 
 	const char* srcMsgIdString, nsIMsgFolder* dstFolder,

mailnews/imap/src/nsImapUndoTxn.h

@@ -38,6 +38,7 @@ class nsImapMoveCopyMsgTxn : public nsMsgTxn
 public:
     NS_DEFINE_STATIC_IID_ACCESSOR(NS_IMAPMOVECOPYMSGTXN_IID)
 
+    nsImapMoveCopyMsgTxn();
     nsImapMoveCopyMsgTxn(nsIMsgFolder* srcFolder, nsMsgKeyArray* srcKeyArray,
                          const char* srcMsgIdString, nsIMsgFolder* dstFolder,
                          PRBool idsAreUids, PRBool isMove,