fix ref count leak of msgdb when marking local msgs read r=naving, sr=sspitzer a=asa 128910

mailnews/db/msgdb/src/nsMailDatabase.cpp

@@ -713,7 +713,7 @@ nsresult nsMailDatabase::SetFolderInfoValid(nsFileSpec *folderName, int num, int
   
   // should we have type safe downcast methods again?
   nsMailDatabase *pMessageDB = (nsMailDatabase *) nsMailDatabase::FindInCache(summaryPath);
-	if (pMessageDB == NULL)
+  if (pMessageDB == nsnull)
   {
     pMessageDB = new nsMailDatabase();
     if(!pMessageDB)
@@ -732,15 +732,12 @@ nsresult nsMailDatabase::SetFolderInfoValid(nsFileSpec *folderName, int num, int
     if (err != NS_OK)
     {
       delete pMessageDB;
-			pMessageDB = NULL;
+      pMessageDB = nsnull;
     }
     bOpenedDB = PR_TRUE;
   }
-	else
-		pMessageDB->AddRef();
   
-
-	if (pMessageDB == NULL)
+  if (pMessageDB == nsnull)
   {
 #ifdef DEBUG
     printf("Exception opening summary file\n");