Blender Git Loki

USD Importer: dependency graph update crash.

Fixed occasional random crash due to simultaneous update
to the dependency graph from multiple threads. A typical
collision might happen when the USD import job thread
is creating a material while the window manager in the
main thread is processing event notifiers. The current
fix is to remove the ND_FRAME flag from the call to
WM_jobs_timer(), which prevents ED_update_for_newframe()
from being called from wm_event_do_notifiers().