Blender Git Loki

Fix T50230: Rigid Body simulation shouldn't step when time is beyond cached area

This makes the last time (`ltime`) stored in the rigid body world (`rbw`)
only be updated once a simulation step actually occurs, this prevents
another simulation step from being solved unless the current time is
exactly one frame after the last cached frame. Thus this prevents the
formation of gaps in the cache, such as seen in T50230.

Reviewers: mont29, sergey, angavrilov

Tags: #physics

Maniphest Tasks: T50230

Differential Revision: https://developer.blender.org/D2458