libobs: Fix transition start during active transition

[Dankirk]

Description

Fixes obs_transition_start() using outdated info to configure new transition if transition was already active.

Here's a snippet from obs-source-transition.c of what needs re-initializing / checking after obs_transition_start() calls obs_transition_set()

lock_transition(transition);
same_as_source = dest == transition->transition_sources[0];
same_as_dest = dest == transition->transition_sources[1];
same_mode = mode == transition->transition_mode;
active = transition_active(transition);
unlock_transition(transition);

if (same_as_source && !active)
	return false;
if (active && mode == OBS_TRANSITION_MODE_MANUAL && same_mode && same_as_dest)
	return true;

Knowing obs_transition_set() will set the dest as source, we should also check for same_as_dest before interrupting current transition since if it is same, it would appear as the transition just turned into a cut. (transition cancel + then having same source and dest).

Motivation and Context

After pr #12622 slideshow fails to fade black/transparent with Stop if used during active transition of slides and instead the last image is shown. This works in 32.0.4.

How Has This Been Tested?

Used slideshow to check transitions work again.

Needs testing with the general transition controls.

Types of changes

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• My code has been run through clang-format.
• I have read the contributing document.
• My code is not on the master branch.
• The code has been tested.
• All commit messages are properly formatted and commits squashed where appropriate.
• I have included updates to all appropriate documentation.

[Warchamp7]

After pr #12622 slideshow fails to fade black/transparent with Stop if used during active transition of slides and instead the last image is shown. This works in 32.0.4.

I am not able to reproduce this issue

Nevermind, the aformentioned change was not in the beta I was testing