Blender Git Loki

Modifiers: Correct deform-only modifiers

There was a discontinuity between how deform-only modifiers are applied
for the case when result deform mesh is requested and when it is not.

Namely, the input mesh will always be guaranteed to present in the
former case, but not in the latter.

This change makes it so input mesh to deform-only modifiers is always
at consistent state.

Pair programming and review together with Bastien, thanks!