Reland "Fix check in GrGLGpu for whether PBO 0 is bound"

This is a reland of 62d42db2829d8f679afdb4fcfbbd7fc2948fea23

Check for PBO support before binding PBO 0.

Original change's description:
> Fix check in GrGLGpu for whether PBO 0 is bound
>
> Found in OOP-R canvas in Chrome. Most likely async read followed by
> sync read with an intervening resetContext().
>
> Bug: chromium:1208212
>
> Change-Id: Ibf85f070d0a4cd389f67e9b249655b0ef667c66e
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/435277
> Commit-Queue: Brian Salomon <bsalomon@google.com>
> Commit-Queue: Robert Phillips <robertphillips@google.com>
> Auto-Submit: Brian Salomon <bsalomon@google.com>
> Reviewed-by: Robert Phillips <robertphillips@google.com>
> Reviewed-by: John Stiles <johnstiles@google.com>

Bug: chromium:1208212
Change-Id: I0da48fa9a1f31ec15827f9bef980e9d5a7d70d26
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/435622
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
3 files changed