//两个list合并处理
/unreadMsgList = unreadMsgList.Union(list).ToList();
//合并处理[MsgCount]
unreadMsgList.ForEach(c =>
{
var group = unreadMsgList.Where(a => a.SenderMark == c.SenderMark);
c.MsgCount = group.Sum(x => x.MsgCount);
});
//去重复
unreadMsgList = unreadMsgList.Distinct().ToList();