When using grease pencil in a stereo rendering the grease pencil objects are only visible in the left eye. In the viewport it renders both.
Issue is related that `DRW_render_gpencil` only renders a single view. But `DRW_render_to_image` renders all views. Aftetr adding a similar loop it renders.
##TODO##
* [] I detected a memory leak of 2 GPU textures. Not sure where they come from, but I will investigate.