Add special resource type for A8_UNORM. Closes #1426

* While it's redundant this format is still valid in D3D so needs to be handled
  correctly.

qrenderdoc/Code/FormatElement.cpp

@@ -657,6 +657,7 @@ QString FormatElement::GenerateTextureBufferFormat(const TextureDescription &tex
     case ResourceFormatType::YUV10:
     case ResourceFormatType::YUV12:
     case ResourceFormatType::YUV16: baseType = lit("xshort4"); break;
+    case ResourceFormatType::A8:
     case ResourceFormatType::S8:
     case ResourceFormatType::Undefined: baseType = lit("xbyte"); break;
   }