The "cuda_mem_map_mutex" was potentially being locked recursively during the call to
"CUDADevice::move_textures_to_host", which crashed. This moves around the locking and
unlocking of "cuda_mem_map_mutex", so that it doesn't call a function that locks it while
still holding the lock.
Reviewed By: pmoursnv
Maniphest Tasks: T85089, T84734
Differential Revision: https://developer.blender.org/D10219
4fbeb3e6be