message: Fix handling of saving cubemaps to disk in GL
  * GL needs special handling because cubemaps need to be treated partially as
  arrays to select the target, then not as arrays when the data is retrieved.
diff: @@ -2421,6 +2421,10 @@ void GLReplay::GetTextureData(ResourceId tex, const Subresource &sub,
  height = 1;
  arraysize = texDetails.height;
  }
  + if(texType == eGL_TEXTURE_CUBE_MAP)
  + {
  + arraysize = 6;
  + }
  }
  s.sample = RDCMIN(uint32_t(texDetails.samples - 1), s.sample);
  @@ -2738,6 +2742,10 @@ void GLReplay::GetTextureData(ResourceId tex, const Subresource &sub,
  RDCASSERT(s.slice < ARRAY_COUNT(targets));
  target = targets[s.slice];
  +
  + // we've "used" the slice, it's not actually a real slice anymore...
  + s.slice = 0;
  + arraysize = 1;
  }
  size_t dataSize = 0;
  