StackHandlers form a chain, where the last element is nullptr,
so calling "handler->next()->foo()" is unsafe because "foo"
might see "this == nullptr".

Bug: v8:3770
Change-Id: Ic989384fa192e29d4d8cb76ff01b32173bf55fd9
Reviewed-on: https://chromium-review.googlesource.com/c/1400406Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58619}