fix reading of online name from folder cache, sr=mscott, needed for 385017 to work on trunk

mailnews/imap/src/nsImapMailFolder.cpp

@@ -1811,7 +1811,7 @@ NS_IMETHODIMP nsImapMailFolder::ReadFromFolderCacheElem(nsIMsgFolderCacheElement
       && hierarchyDelimiter != kOnlineHierarchySeparatorUnknown)
     m_hierarchyDelimiter = (PRUnichar) hierarchyDelimiter;
   rv = element->GetStringProperty("onlineName", onlineName);
-  if (NS_SUCCEEDED(rv) && +onlineName.IsEmpty())
+  if (NS_SUCCEEDED(rv) && !onlineName.IsEmpty())
     m_onlineFolderName.Assign(onlineName);
 
   m_aclFlags = -1; // init to invalid value.