Edwin Pujols authored Dec 13, 2020 and Tomaz Canabrava committed Dec 18, 2020

The code commented with `nowrap!` has no use: `_cuX` and `_cuY` get
updated to this value on image resize. This code also appeared in
functions unrelated to horizontal wrapping.

I also took the liberty to update the conditions which determine whether
to use "default values". Before, the conditions only checked for zero
instead of (invalid) negative numbers (maybe a few Q_ASSERT's are
desired here?).