Check if pdev is NULL in xf86PlatformDeviceCheckBusID

Looks like pdev would be NULL for vgem/vkms devices.

Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>
4 jobs for master in 13 minutes and 7 seconds (queued for 1 second)
latest
Status Name Job ID Coverage
  Docker Image
passed debian-buster #5978238

00:05:56

 
  Build And Test
passed autotools #5978239

00:07:10

passed meson #5978240

00:02:09

passed meson-noglamor #5978241

00:01:54