Fix XChangeFeedbackControl() request underflow

CVE-2021-3472 / ZDI-CAN-1259

This vulnerability was discovered by:
Jan-Niklas Sohn working with Trend Micro Zero Day Initiative

Signed-off-by: Matthieu Herrb <matthieu@herrb.eu>
4 jobs for master in 4 minutes and 46 seconds (queued for 4 seconds)
Status Job ID Name Coverage
  Docker Image
passed debian-buster #8820741

00:00:16

 
  Build And Test
passed autotools #8820742

00:04:29

passed meson #8820743

00:02:03

passed meson-noglamor #8820744

00:02:14