Blender Git Loki

Asset View: Always show all poses, avoid double-scrollbar

The asset view so far showed up to 5 items by default. If there were
more assets to be shown than that, it the list would become scrollable.
This would cause a scrollable box inside a scrollable region, which is
not nice for interaction. We can just expand the list so all assets are
in the layout, and the user can scroll the region rather than scrolling
the list.

Also hide the "grip" button so the list can't be resized. If needed we
could allow making the list smaller still, even if that causes double
scrolling again. For now keeping it simple.
Had to add a "no grip" option for that, so I changed the signature a bit
to avoid too many boolean arguments.

And another also: Adds missing return after error check.