[GN fuzzer] Stack overflow fix.

Fuzzathon 2017.

Bug: 648076,749793,773426,768111,754972,734401,734200
Change-Id: Ic608c5a374252809443a879ad4e2ddf8f6184697
Reviewed-on: https://chromium-review.googlesource.com/736159
Commit-Queue: Penny MacNeil <pennymac@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Reviewed-by: Max Moroz <mmoroz@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#512626}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 697f302d91e7ad4466416ab22c290c7fea9c6b93