Looks like a left-over pending exception from a previous fuzzer run on the same Isolate.

I'll take a look ...

The following revision refers to this bug:
  https://chromium.googlesource.com/v8/v8.git/+/c63f1051e3c7fa4c252e7cb3cff8d7530fbeb746

commit c63f1051e3c7fa4c252e7cb3cff8d7530fbeb746
Author: Michael Starzinger <mstarzinger@chromium.org>
Date: Tue May 02 10:31:32 2017

[fuzzer] Make parser fuzzer handle pending exceptions.

This ensures exceptions thrown during parsing are properly propagated
into the surrounding {v8::TryCatch} block. Otherwise running more than
one test input in the same Isolate can fail due to pending exceptions. 

R=jochen@chromium.org
BUG= chromium:715037 

Change-Id: Iaa5735515dc097d8cb12dcf8672451f3c9503440
Reviewed-on: https://chromium-review.googlesource.com/490047
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Jochen Eisinger <jochen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45019}
[modify] https://crrev.com/c63f1051e3c7fa4c252e7cb3cff8d7530fbeb746/src/isolate.h
[modify] https://crrev.com/c63f1051e3c7fa4c252e7cb3cff8d7530fbeb746/test/fuzzer/parser.cc

ClusterFuzz has detected this issue as fixed in range 468615:468644.

Detailed report: https://clusterfuzz.com/testcase?key=6470105388285952

Fuzzer: libfuzzer_v8_script_parser_fuzzer
Job Type: libfuzzer_chrome_asan_debug
Platform Id: linux

Crash Type: CHECK failure
Crash Address: 
Crash State:
  Disposing the isolate that is entered by a thread in isolate.cc
  
Sanitizer: address (ASAN)

Regressed: https://clusterfuzz.com/revisions?job=libfuzzer_chrome_asan_debug&range=455091:455226
Fixed: https://clusterfuzz.com/revisions?job=libfuzzer_chrome_asan_debug&range=468615:468644

Reproducer Testcase: https://clusterfuzz.com/download?testcase_id=6470105388285952


See https://chromium.googlesource.com/chromium/src/+/master/testing/libfuzzer/reproducing.md for more information.

If you suspect that the result above is incorrect, try re-doing that job on the test case report page.