Fix MASMonitor screen camera wiping display when IVA is inactive

[kilfoil]

Problem

When the active vessel switches (e.g. a crew member goes on EVA, or you switch to another vessel), KSP calls OnBecomeInactive() on all InternalModule instances. MASMonitor does not override this method.

The monitor's screenCamera is left enabled with ClearFlags.SolidColor and an opaque-black backgroundColor. With targetTexture no longer pointing to a live render texture, Unity falls back to rendering the camera to the main display. This wipes the skybox and scaled-space bodies (Mun, Kerbin, stars, etc.) every frame until the vessel is reactivated.

Fix

Override OnBecomeInactive() to disable screenCamera, and OnBecomeActive() to re-enable it. The monitor has nothing to render when the IVA is inactive, so disabling the camera is correct behaviour.

public override void OnBecomeInactive()
{
    if (screenCamera != null)
    {
        screenCamera.enabled = false;
    }
}

public override void OnBecomeActive()
{
    if (screenCamera != null)
    {
        screenCamera.enabled = true;
    }
}

Reproduction

1. Board a vessel that has a JSI BasicMFD prop using MASMonitor
2. Have a crew member go on EVA, or switch to another vessel
3. Observe: background goes black; skybox, Mun, Kerbin all invisible
4. Switch back to the vessel: display returns to normal