This issue happend when a geometry nodes modifier wouldn't output grease
pencil geometry. In this case, we write an emtpy grease pencil
data-block to the evaluated `geometry_set`. But we don't update the
`eval_frame` that indicates on what frame the grease pencil data-block
was evaluated on.
The fix makes sure we update the `eval_frame` even if the output is
empty.
Additionally, there was a missing return in the
`get_evaluated_grease_pencil_drawing_deformation` function that lead
to an empty `deformation.positions` span.
The fix makes sure we return the correct deformation with the correct
positions.
Falk David
ab652f7b5f