Blender Git Loki

Fix T67127: Crash Missing DEG tag update mask layer

When ng mask layer operations (add, remove, move) the
original mask was not tagged to be updated resulting
in missing data on the copy. The Masking function
assumes that the copy and the original is always
structured the same.

Reviewed By: brecht, sergey

Differential Revision: https://developer.blender.org/D5283