root_scratchpad_hide: fix crash when layer focused
root_scratchpad_hide: fix crash when layer focused

This fixes a crash in `root_scratchpad_hide` when a layer surface is
focused. Since `seat_get_focus` is NULL when a layer surface is
focused, the call to `node_has_ancestor` was causing a SIGSEGV since it
was attempting to access the parent of NULL. This changes the call to
`seat_get_focus_inactive`, which will return a node even when a layer
surface is focused and is also guaranteed to have something in the
focus stack if a scratchpad container is being hidden (otherwise there
would not be any containers yet).

SirCmpwn/sway,1ace/sway,1ace/sway,ascent12/sway,ascent12/sway,1ace/sway,ascent12/sway