Fix scratchpad fullscreen behavior and crash

When setting fullscreen on a hidden scratchpad container, there was a
check to see if there was an existing fullscreen container on the
workspace so it could be fullscreen disabled first. Since the workspace
is NULL, it would cause a SIGSEGV. This adds a NULL check to avoid the
crash.

This also changes the behavior of how fullscreen is handled when adding
a container to the scratchpad or changing visibility of a scratchpad
container to match i3's. The behavior is as follows:
- When adding a container to the scratchpad or hiding a container back
  into the scratchpad, there is an implicit fullscreen disable
- When setting fullscreen on a container that is hidden in the
  scratchpad, it will be fullscreen when shown (and fullscreen disabled
  when hidden as stated above)
- When setting fullscreen global on a container that is hidden in the
  scratchpad, it will be shown immediately as fullscreen global. The
  container is not moved to a workspace and remains in the
  scratchpad. The container will be visible until fullscreen disabled
  or killed. Since the container is in the scratchpad, running
  `scratchpad show` or `move container to scratchpad` will have no
  effect

This also changes `container_replace` to transfer fullscreen and
scratchpad status.

1 files changed, 5 insertions, 0 deletions

diff --git a/include/sway/input/seat.h b/include/sway/input/seat.h
index f2af1066..eb6c09a1 100644
--- a/include/sway/input/seat.h
+++ b/include/sway/input/seat.h
@@ -143,6 +143,11 @@ struct sway_node *seat_get_focus(struct sway_seat *seat);
 
 struct sway_workspace *seat_get_focused_workspace(struct sway_seat *seat);
 
+// If a scratchpad container is fullscreen global, this can be used to try to
+// determine the last focused workspace. Otherwise, this should yield the same
+// results as seat_get_focused_workspace.
+struct sway_workspace *seat_get_last_known_workspace(struct sway_seat *seat);
+
 struct sway_container *seat_get_focused_container(struct sway_seat *seat);
 
 /**