|scope_snapshot_| might not have been cleared if there was a parser error between setting
the snapshot and consuming it. Explicitly clear it at the end of parsing for that case.
Otherwise Scope::Snapshot's destructor will possibly write into the already freed zone.

Bug: chromium:909976
Change-Id: I8469d11f04e7f71528be5cba5663c652cd7eacb2
Reviewed-on: https://chromium-review.googlesource.com/c/1354880
Commit-Queue: Toon Verwaest <verwaest@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57938}