This CL enables use of a bound buffer at TexSubImage2D by allowing nil (0) data, which indicates the head of the bound buffer. In the long run, we need to be able to pass non-0 integer to not only TexSubImage2D but also other functions like TexImage2D. As we might change the API, let's revisit this issue later. Fixes golang/go#36355 Change-Id: I66f6650b10fca9a346cfa6eba246ea9286ed3a85 Reviewed-on: https://go-review.googlesource.com/c/mobile/+/213077 Run-TryBot: Hajime Hoshi <hajimehoshi@gmail.com> Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>