va_trace: avoid to dereference a NULL pointer
va_trace: avoid to dereference a NULL pointer

Signed-off-by: Xiang, Haihao <8d677183e5993577d4fa73a419b76987913292d6@intel.com>
(cherry picked from commit e635bf060b68694174cbf24c6b06c573b629ddcc)

01org/iotg-lin-gfx-libva,01org/libva-cros,chenxianqin/vaapi-libva,gbeauchesne/libva,zzhhui/libva,01org/libva-cros,pma1/libva,01org/libva-cros,pma1/libva,gbeauchesne/libva,pma1/libva,01org/iotg-lin-gfx-libva,chenxianqin/vaapi-libva,zzhhui/libva,gbeauchesne/libva,01org/iotg-lin-gfx-libva,zzhhui/libva,chenxianqin/vaapi-libva