导航按钮添加UIBarButtonSystemItemFixedSpace，返回时标题消失

[jackliuheh]

UIBarButtonItem *leftItemSetting = [[UIBarButtonItem alloc]
                                     initWithImage:[[UIImage imageNamed:@"setting_icon"]imageWithRenderingMode:UIImageRenderingModeAlwaysOriginal] style:UIBarButtonItemStylePlain target:self action:@selector(mineSettingEvent:)];
UIBarButtonItem *rightItemMessage = [[UIBarButtonItem alloc]
                              initWithImage:[[UIImage imageNamed:@"mine_message_icon"]imageWithRenderingMode:UIImageRenderingModeAlwaysOriginal] style:UIBarButtonItemStylePlain target:self action:@selector(mineMessageEvent:)];
UIBarButtonItem *spaceItem = [[UIBarButtonItem alloc]initWithBarButtonSystemItem:UIBarButtonSystemItemFixedSpace target:nil action:nil];
self.navigationItem.leftBarButtonItem = leftItemSetting;
self.navigationItem.rightBarButtonItems = @[rightItemMessage,spaceItem,rightItemEye];