Relax detection of non-premultiplied alpha cursor data

The stricter detection broke the cursor in some games. Apparently those
use cursor data with premultiplied alpha, but with some pixels having
r/g/b values larger than the alpha value (which corresponds to original
r/g/b values > 1.0), triggering the workaround.

Relax the detection to match what's in the X server since 1.18.4, but
keep the workaround for older versions.

Bugzilla: https://bugs.freedesktop.org/108650
Acked-by: Alex Deucher <alexander.deucher@amd.com>
11 jobs for relax-non-premul-alpha-cursor-detection in 3 minutes and 27 seconds (queued for 2 minutes and 41 seconds)
Status Job ID Name Coverage
  Build
passed #44516
xserver-1.13

00:00:32

passed #44517
xserver-1.14

00:00:37

passed #44518
xserver-1.15

00:00:34

passed #44519
xserver-1.16

00:00:30

passed #44520
xserver-1.17

00:00:30

passed #44521
xserver-1.18

00:00:29

passed #44522
xserver-1.18-clang

00:00:33

passed #44523
xserver-1.19

00:00:30

passed #44524
xserver-1.19-clang

00:00:33

passed #44514
xserver-1.20

00:00:39

passed #44515
xserver-1.20-clang

00:00:37