Allow invaid surface to be passed as reference surface

The driver handles this case and runs other filters if references are
not supplied properly. This is better than falling back to the
unprocessed surface. The fallback is done in other error cases though.

video.c

@@ -1622,6 +1622,9 @@ static VAStatus VaapiPostprocessSurface(VAContextID ctx, VASurfaceID src, VASurf
 
     /* Skip postprocessing if queue is not deinterlaceable */
     for (i = 0; i < *num_brefs; ++i) {
+	// Trust the driver to "do the right thing" if invalid surfaces are provided as references
+	if (brefs[i] == VA_INVALID_ID)
+	    continue;
 	va_status = vaQuerySurfaceStatus(VaDisplay, brefs[i], &va_surf_status);
 	if (va_status != VA_STATUS_SUCCESS) {
 	    Error("vaapi/vpp: Surface %d query status failed (0x%X): %s", i, va_status, vaErrorStr(va_status));
@@ -1634,6 +1637,9 @@ static VAStatus VaapiPostprocessSurface(VAContextID ctx, VASurfaceID src, VASurf
     }
 
     for (i = 0; i < *num_frefs; ++i) {
+	// Trust the driver to "do the right thing" if invalid surfaces are provided as references
+	if (frefs[i] == VA_INVALID_ID)
+	    continue;
 	va_status = vaQuerySurfaceStatus(VaDisplay, frefs[i], &va_surf_status);
 	if (va_status != VA_STATUS_SUCCESS) {
 	    Error("Surface %d query status = 0x%X: %s", i, va_status, vaErrorStr(va_status));