add nil judge

[ashen-zhao]

• (MB_INSTANCETYPE)showHUDAddedTo:(UIView )view animated:(BOOL)animated { if (view == nil) { return nil; } MBProgressHUD hud = [[self alloc] initWithView:view]; hud.removeFromSuperViewOnHide = YES; [view addSubview:hud]; [hud show:animated]; return MB_AUTORELEASE(hud); }

ps: Add empty type judgment, In order to avoid crash when view's parameter is nil