Adjust the FBO invalidate attachment enums for emulated default FBOs. BUG=angleproject:1953 Change-Id: I7f325e3b7400e12077cdf9106a83a747a318a299 Reviewed-on: https://chromium-review.googlesource.com/461297 Reviewed-by: Geoff Lang <geofflang@chromium.org> Commit-Queue: Geoff Lang <geofflang@chromium.org>