Fix passthru copy when input X2RGB10 with a2rgb10 pointer

If input use only a2rgb10 pointer and we get min pointer, this leads to
nullptr error. Since a2rgb10(x2rgb10) packed 10 bit format, no need to
check all pointers before copy, we only need to copy B pointer (that is
in union with a2rgb10 pointer).

cmd to check:
./ffmpeg -hwaccel qsv -v verbose -c:v hevc_qsv -i \
  ../p010.h265 -vf scale_qsv=format=x2rgb10,hwdownload,format=x2rgb10 \
  -vframes 1 out.yuv -y

fixes: Intel-Media-SDK#1654

_studio/shared/src/libmfx_allocator_vaapi.cpp

@@ -1,4 +1,4 @@
-// Copyright (c) 2017-2019 Intel Corporation
+// Copyright (c) 2017-2020 Intel Corporation
 //
 // Permission is hereby granted, free of charge, to any person obtaining a copy
 // of this software and associated documentation files (the "Software"), to deal
@@ -515,6 +515,7 @@ mfxStatus mfxDefaultAllocatorVAAPI::SetFrameData(const VAImage &va_image, mfxU32
         break;
 #ifndef ANDROID
     case VA_FOURCC_A2R10G10B10:
+    case VA_FOURCC_X2R10G10B10:
         if (mfx_fourcc == MFX_FOURCC_A2RGB10)
         {
             ptr->B = p_buffer + va_image.offsets[0];

_studio/shared/src/libmfx_core.cpp

@@ -1497,7 +1497,6 @@ mfxStatus CoreDoSWFastCopy(mfxFrameSurface1 *pDst, mfxFrameSurface1 *pSrc, int c
     case MFX_FOURCC_AYUV:
     case MFX_FOURCC_RGB4:
     case MFX_FOURCC_BGR4:
-    case MFX_FOURCC_A2RGB10:
         {
             mfxU8* ptrSrc = std::min({pSrc->Data.R, pSrc->Data.G, pSrc->Data.B});
             mfxU8* ptrDst = std::min({pDst->Data.R, pDst->Data.G, pDst->Data.B});
@@ -1508,6 +1507,12 @@ mfxStatus CoreDoSWFastCopy(mfxFrameSurface1 *pDst, mfxFrameSurface1 *pSrc, int c
             MFX_CHECK_STS(sts);
             break;
         }
+case MFX_FOURCC_A2RGB10:
+            roi.width *= 4;
+
+            sts = FastCopy::Copy(pDst->Data.B, dstPitch, pSrc->Data.B, srcPitch, roi, copyFlag);
+            MFX_CHECK_STS(sts);
+            break;
     case MFX_FOURCC_ARGB16:
     case MFX_FOURCC_ABGR16:
         {