PointerDragBehavior: Added check to force releaseDrag to fire when no active button is present

[PolygonalSun]

A user on the forum found an issue where if a user programmatically started a drag event, they could not release it with a click. Using their provided solution, this PR contains the following fix. A check was added to the POINTERUP section to just force the release if there is no active button (thanks to mattdmorgan for the fix recommendation).

Forum Link: https://forum.babylonjs.com/t/programmatically-started-drags-can-no-longer-be-completed-by-clicking/38228

[bjsplat]

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[bjsplat]

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