Tiled windows are kept when outputs are removed, but don't account for panel

In Xfwm4-4.16.1, tiled windows are transferred to the remaining output when the output they were on is removed. However, this doesn't account for panels.

Repro:

• Two active outputs, X and Y, with Y set as primary
• Panel set to remain on primary and "Don't reserve space on borders" unchecked
• Random window tiled to left half of Y
• Disable Y
• Panel moves to X
• Window moves to left half of X -> Window will occupy space behind the panel on X

Manually re-tiling the window restores proper behavior (respecting panel boundary)

Thanks!