Fix MASMonitor screen camera rendering to main display when IVA is inactive

When the active vessel switches (e.g. crew goes on EVA), KSP calls
OnBecomeInactive() on all InternalModules. MASMonitor's screenCamera
is left enabled with ClearFlags.SolidColor and an opaque-black background,
so it renders to the main screen every frame, wiping the skybox and
scaled-space bodies (Mun, Kerbin, etc.) until the vessel is reactivated.

Fix: override OnBecomeInactive() to disable screenCamera, and
OnBecomeActive() to re-enable it.

Author: kilfoil

Source/MASMonitor.cs

@@ -344,6 +344,30 @@ public void OnDestroy()
             }
         }
 
+        /// <summary>
+        /// Disable the screen camera when the IVA becomes inactive (e.g. on EVA or vessel switch).
+        /// Without this, the camera renders to the main screen with its opaque-black SolidColor
+        /// clear, wiping the skybox and scaled-space bodies every frame.
+        /// </summary>
+        public override void OnBecomeInactive()
+        {
+            if (screenCamera != null)
+            {
+                screenCamera.enabled = false;
+            }
+        }
+
+        /// <summary>
+        /// Re-enable the screen camera when the IVA becomes active again.
+        /// </summary>
+        public override void OnBecomeActive()
+        {
+            if (screenCamera != null)
+            {
+                screenCamera.enabled = true;
+            }
+        }
+
         /// <summary>
         /// Just in case we lose context.
         /// </summary>