Delay grease pencil for until after the render result is written
to the Blender side.

Includes the following commits:

• Fix Cycles using Cancel semantic on final result write

Seems like a copy-paste bug from another place.

• Fix Cycles allocating result too early

When tiled rendering was used the render result was
allocated at the end of every view layer render as
opposite of an intended end of all rendering.

Modify the render_result_end so that it only ensures
pixels are allocated if pixels are actually copied
over.