Fix crash on source resize while Replay Buffer is active (#166)

[romanrafael12]

Hi exeldro,

I ran into the crash described in #166 and tracked down the cause.
This PR fixes it.

The problem

When a source's resolution changes while a Source Record filter has
the Replay Buffer enabled (for example, tabbing in/out of a window
capture), OBS crashes.

source_record_filter_tick() recreated the obs_view / video_output
by calling obs_view_remove() immediately on a size change — while the
encoder was still feeding from the old video_output and the replay
buffer output was still running. The encoder kept pulling frames from a
freed video_output, causing a use-after-free crash.

Three related issues:

1. video_output destroyed while in use — obs_view_remove() ran
   synchronously on a size change, even with outputs/encoder still active.
2. encoder released while active — update_encoder() called
   obs_encoder_release() without checking obs_encoder_active() first
   (release_encoders() already does this check, so it was inconsistent).
3. race on async restart — new outputs could start (reusing the
   encoder) while a previous output was still being force-stopped.

The fix

• On a size change with active outputs, only set restart = true and
  defer recreation. video_output is recreated only once outputs are
  down and the encoder is idle.
• update_encoder() no longer releases an active encoder, and re-points
  the encoder to the current video_output when reusing an idle one.
• The output-start path waits until any previous encoder has fully wound
  down before starting new outputs.

44 lines changed; no behavior change for the normal start/stop path.

Testing

Tested on Windows with OBS 32.1.2. Ran 8 simultaneous Source Record
filters with Replay Buffer enabled for ~37 minutes — 100+ replay saves,
repeated scene switches and source resizes. No crashes, clean shutdown.
The same scenario reliably crashed before the patch.

Thanks for the plugin!