Don't reuse failed buffers as scratch

This is/was occurring for ANGLE D3D configs

Change-Id: I45d4c40143ce4ac4989612c7bfe7aefd178842da
Reviewed-on: https://skia-review.googlesource.com/19076
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
2 files changed