FXBlurView crash when close the photo's authorization of the project while app running

[peiyun007]

When Using FXBlurView in my project,

    FXBlurView *blurView = [[FXBlurView alloc] initWithFrame:self.view.bounds];
    blurView.tintColor = [UIColor clearColor];
    blurView.blurRadius = 1;
    blurView.iterations = 20;
    blurView.tintColor = [UIColor colorWithWhite:0 alpha:0.5f];
    blurView.updateInterval = 0.1f;
    [self.view addSubview:blurView];

When the app is running, I switch to the background and turn off the photo's authorization of the app,then FXBlurView crash.Below is the crash stack.