Frame Capture: Don't unmap regenned buffers in reset. These buffers are deleted and recreated, so unmapping them gives a "resource not mapped" error during replay. Found when working on the "world_war_doh" trace. Bug: angleproject:5133 Change-Id: Id1e6318c44a2a09fa643ef0a72f1d03d8396e5fb Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3327862 Reviewed-by: Tim Van Patten <timvp@google.com> Reviewed-by: Cody Northrop <cnorthrop@google.com> Commit-Queue: Jamie Madill <jmadill@chromium.org>