Fix Guider capture/reacquire timeout handling

This MR fixes an issue with the capture timeout handler of the Guide module, which attempts to capture a frame when there is a failure event reported even if the guider is external.

When using PHD2, the Ekos Guide module reacts to star-lost events by issuing a new capture, which conflicts with PHD2 activity.

In my case, PHD2 is using subframes, so Guide unexpectedly receives a small frame, but does not react, which triggers the capture timeout event, which removes the CCD driver and reconnects it.

In my case again, both CCD are managed by the Atik driver. Thus, PHD2 dies when the guiding camera driver disappears, and Ekos dies when Scheduler restarts capturing on the main camera.