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It fix T46381. Normally BL_Action::Update (manage action time, end, loop…) should be called the same number of times as BL_Action::UpdateIPO (update action position, scale ect… in the game object).
But the bug report shows that UpdateIPO is called one less time than Update. To fix it i revert the commit 362b25b382 and implement a mutex in BL_Action::Update.
Example file : {F245823}
Reviewers: lordloki, kupoman, campbellbarton, youle, moguri, sybren
Reviewed By: youle, moguri, sybren
Maniphest Tasks: T39928, T46381
Differential Revision: https://developer.blender.org/D1562