Blender Git Loki

Fix crash opening files saved in sculpt/vertex paint modes

Skip access to any evaluated data when operator is run on file load,
we don't have depsgraph evaluated yet. In this case we skip part of
sculpt session initialization, since it will be done during depsgraph
evaluation which happens after DEG_on_visible_update().

We can not skip sculpt session initialization since during normal
operation we want all the data to be initialized on mode change,
and not on initial brush stroke.