When a view unmaps, normally the surviving ancestor (ie. after reaping)
needs to be arranged. When a fullscreen view unmaps, it arranges the
workspace rather than the surviving ancestor, but didn't handle cases
where the workspace itself was reaped. This happens if the workspace is
not currently shown and the fullscreen view was the last container on
that workspace.
This commit rewrites this part of view_unmap so it's more readable, and
fixes the crash by not arranging the workspace if it's been reaped. Note
that it no longer arranges the output under any circumstance - this
wasn't required anyway.
854c5fbec8