If the user has moved the extension dialog, we don't want to re-center it on every single update -- many extensions update their dialogs on every input change, and this behavior can cause the extension dialog to keep re-overlapping with the video, which is very frustrating.
Signed-off-by: Felix Paul Kühne <fkuehne@videolan.org>
(cherry picked from commit ad765c21ffe71fe27b3b6a03ebaa878408ba40ee)

Conflicts:
	modules/gui/macosx/ExtensionsDialogProvider.m