capture_gles_3_2: Set read buffer for glGetPointerv. As required by the GLES1 VertexPointerTest. Bug: angleproject:5751 Change-Id: I889d136a2f76b0b9c256ffc9176c08a8c2b03a08 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2756534 Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Cody Northrop <cnorthrop@google.com> Commit-Queue: Lubosz Sarnecki <lubosz.sarnecki@collabora.com>