va_x11.c::va_DisplayContextGetNumCandidates always returns success

Problem was detected while investigating the crash when running GStreamer pipeline with vaapisink over SSH with X Forwarding.

VA_API version 1.8.0
LibVA 2.8.0

in va_x11.c
```
234 static VAStatus va_DisplayContextGetNumCandidates (
235 VADisplayContextP pDisplayContext,
236 int *num_candidates
237 )
238 {
239 VAStatus vaStatus;
240
241 vaStatus = va_DRI2_GetNumCandidates(pDisplayContext, num_candidates);
242
243 /* A call to va_DisplayContextGetDriverName will fallback to other
244 * methods (i.e. NVCTRL, FGLRX) when DRI2 is unsuccessful. All of those
245 * fallbacks only have 1 candidate driver.
246 */
247 if (vaStatus != VA_STATUS_SUCCESS)
248 *num_candidates = 1;
249
250 return VA_STATUS_SUCCESS;
251 }
```

va_DisplayContextGetNumCandidates always returns SUCCESS status even if the DRI2 is not authed.
Seems like return status is not correct for this case.