[Encode] KW issue fix for encoder g10(CL#778304)

KW issue fix for encoder g10

Change-Id: I1dab578014684a0cd98eea16f07fefd429c4f16f

Author: junyongs

media_driver/agnostic/gen10/codec/hal/codechal_encode_mpeg2_g10.cpp

@@ -2087,7 +2087,11 @@ MOS_STATUS CodechalEncodeMpeg2G10::SendMeSurfaces(
         uint8_t scaledIdx = m_refList[refPicIdx]->ucScalingIdx;
 
         // for 4xMe
-        refScaledSurface.OsResource = m_trackedBuf->Get4xDsSurface(scaledIdx)->OsResource;
+        MOS_SURFACE* p4xSurface = m_trackedBuf->Get4xDsSurface(scaledIdx);
+        if (p4xSurface != nullptr)
+        {
+            refScaledSurface.OsResource = p4xSurface->OsResource;
+        }
         refScaledBottomFieldOffset = refBottomField ? (uint32_t)m_scaledBottomFieldOffset : 0;
 
         // L1 Reference Picture Y - VME