[tools] Change CoreDumpArchiver to not default throw
[tools] Change CoreDumpArchiver to not default throw

This prevents missing core dumps from crashing bots a la:
https://logs.chromium.org/logs/dart/buildbucket/cr-buildbucket.appspot.com/8846992204042276416/+/u/vm_tests_shard_1/task_stdout_stderr:_vm_tests_shard_1

Bug: https://github.com/dart-lang/sdk/issues/36469
Change-Id: If66e40d8cb2df7ece7c1274fbbdcbffda445056d
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/200865
Reviewed-by: Vyacheslav Egorov <72c81f38df725d8f1832acb9b5bb99563fc2f1b9@google.com>
Commit-Queue: Clement Skau <495593248b6158163719b90dde8357b589c8e5d0@google.com>

dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk