Don't set SourceValidate pointer to NULL
inspired from similar code in amdgpu, fixes a crash when xrandr(1) is invoqued with X server 21.1.1 Signed-off-by: Matthieu Herrb <matthieu.herrb@laas.fr>
inspired from similar code in amdgpu, fixes a crash when xrandr(1) is invoqued with X server 21.1.1 Signed-off-by: Matthieu Herrb <matthieu.herrb@laas.fr>