workspace: ignore not_this_one if not in current workspace

When the active workspace is changed, marco figures out which window
should get focus by calling `focus_ancestor_or_top_window`. In some
cases that call might include a window that should not get focus as
`not_this_one`.

When `not_this_one` refers to a window, the function will check to see
if it has a parent, and if it does, it will ignore the new workspace's
`mru_list` and will focus that parent window. However, it doesn't check
to see if the parent window is actually on the new workspace. If the
parent isn't on the new workspace, focusing it will drag it over,
including the transient window that was supposed to be ignored. This
isn't the result a user would likely expect, and is made more confusing
by the parent window being minimized, stuck that way until the user
switches to another workspace and back.

This change makes `focus_ancestor_or_top_window` ignore the
`not_this_one` window if it isn't on the new workspace's `mru_list`.
Instead it will just search the new workspace's `mru_list` for a window
to focus.

src/core/workspace.c

@@ -1049,8 +1049,9 @@ focus_ancestor_or_top_window (MetaWorkspace *workspace,
     meta_topic (META_DEBUG_FOCUS,
                 "Focusing MRU window\n");
 
-  /* First, check to see if we need to focus an ancestor of a window */
-  if (not_this_one)
+  /* First, check to see if we need to focus an ancestor of a window
+   * that exists in this workspace */
+  if (not_this_one && g_list_find (workspace->mru_list, not_this_one) != NULL)
     {
       MetaWindow *ancestor;
       ancestor = NULL;