libobs, UI: Fix cpp auto-release assignment from OBSRefs

The *AutoRelease helpers should not take references from OBSRef objects.
Instead, make an OBSRefAutoRelease base class, and OBSRef a subclass of
that to allow moves, and then perform moves from those objects.

This fixes an issue where *AutoRelease OBSRef objects would cause an
unintended double release of objects after having been assigned values
from non-*AutoRelease OBSRef objects.

UI/window-basic-main-transitions.cpp

@@ -403,9 +403,9 @@ void OBSBasic::TransitionToScene(OBSSource source, bool force,
 		OBSSource trOverride = GetOverrideTransition(source);
 
 		if (trOverride && !overridingTransition && !quickTransition) {
-			transition = trOverride;
+			transition = std::move(trOverride);
 			duration = GetOverrideTransitionDuration(source);
-			OverrideTransition(trOverride);
+			OverrideTransition(transition.Get());
 			overridingTransition = true;
 		}
 
@@ -974,7 +974,7 @@ void OBSBasic::TBarChanged(int value)
 			OverrideTransition(tBarTr);
 			overridingTransition = true;
 
-			transition = tBarTr;
+			transition = std::move(tBarTr);
 		}
 
 		obs_transition_set_manual_torque(transition, 8.0f, 0.05f);
@@ -1603,8 +1603,7 @@ void OBSBasic::SetPreviewProgramMode(bool enabled)
 					? OBS_SCENE_DUP_PRIVATE_COPY
 					: OBS_SCENE_DUP_PRIVATE_REFS);
 		} else {
-			dup = curScene;
-			obs_scene_addref(dup);
+			dup = std::move(OBSScene(curScene));
 		}
 
 		OBSSourceAutoRelease transition = obs_get_output_source(0);