[graphite] Fix GrSurfaceProxyView::onGenerateTexture
[graphite] Fix GrSurfaceProxyView::onGenerateTexture

Fixing a bug in https://skia-review.googlesource.com/c/skia/+/582501 when in "preAbandonGpuContext" mode

Change-Id: I0aef4b5b7cb65f36f4d9c857990d918f9c8a7440
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/582800
Commit-Queue: Robert Phillips <95e8ac5504948c7bf91b22c16a8dbb7ae7c66bfd@google.com>
Reviewed-by: Jim Van Verth <509afb0bfbb23ecaaf1fb3323209f531b45e75a6@google.com>

google/skia,google/skia,google/skia,google/skia,google/skia,google/skia,google/skia,google/skia,google/skia,google/skia