Fix crash on resize while doing other things
Commits 9ffe33a2 and 4352df00 introduce and use a getScreenLineColumns(line) method to provide support for DECDWL (Double-Width) lines.
It turns out that under some conditions on resize Screen::_cuY (the current cursor Y position) and ScreenWindow::endWindowLine() can have different ideas of how many lines the terminal has.
A test that asserts:
while [ true ]; do echo -e "\e[?1047h"; done Resize the window, making it smaller