All windows disappear if tiling is enabled while an app is hanging

[jacobgkau]

Tested on f75d89b.

If an app is hanging (e.g. #264), and tiling is enabled, then all windows disappear (even ones that were not hanging).

Before pressing Ctrl-Y (both windows visible, COSMIC Term hanging but COSMIC Settings working):

After pressing Ctrl-Y (neither window visible, even though their icons still show them as running in the dock):

You can close this if it's too related to the specific hang in #264, but it would seem ideal that the compositor would still be able to tile/handle properly all the other windows if only one of them is hanging.