Added detection of empty layers so the wipe tower doesn't trip on them (it is not printable anyway).
This should improve wipe tower reliability with supports, objects standing on edges, etc.
I also turned an assert into exception throw to prevent hard crashes and nonsense output.
There was a bug in unit tests that led to generating the wipe tower with non-normalized preset.
This caused out-of-bounds access into max_layer_height vector in fill_wipe_tower_partitions.
The problem surfaced in https://github.com/prusa3d/PrusaSlicer/issues/2288.
I quickly patched additional normalization of the preset to prevent this from happening.
Also, an assert in the same function turned out to trip on one of the tests.
This one was commented out for now and will (hopefully) be looked into later.
Function Print::apply_config was renamed to apply_config_perl_tests_only so everyone
sees its current purpose and does not mistake it for the more important Print::apply.
by PrintObject::region_volumes. This is due to the way Print::apply()
works, it does not invalidate an existing PrintObject if a new region
is added to the print.
