TE: allow Ghostblock triangle flip on ceiling

[LoreRaider]

When using ghostblocks (just like normal geometry) it's possible to flip the triangle by hovering the sector and pressing Alt+Click.
However, the same can't be done with the ceiling.

Repro steps:

• Add a ghostblock on a sector
• Raise or lower one of the 4 vertices of the ghostblock
• Press Alt+Click on the ceiling part of the ghostblock, nothing happens

Expected result: correct flip of the ceiling triangle

As you can see the imported geo rooftop has a different triangle flip than the ghostblock

[Nickelony]

This is already possible. You have to ALT+Click on the ceiling tile, rather than the ghost block itself. It's the exact same for floor tiles.