Strange behaviour after window resize with saveLines=0

[Bert Münnich]

Hi,

after installing rxvt-unicode version 9.16 I've noticed a strange
behaviour after resizing the window, if the "saveLines" X resource is
set to "0": When new output is generated and the buffer's text is
scrolled, old content repeatedly re-enters the screen from below and
is mixed with the new output. Version 9.15 does not show this
behaviour.

Steps to reproduce this issue:
1. Open a new instance of rxvt-unicode with `-sl 0`
2. Add some text to the buffer, e.g. `ls -l`
3. Resize the window, regardless of direction and amount
4. Repeatedly hit return, after cursor line reaches end of screen old
text from above re-enters the screen from below

Thanks for looking into this.

Bert