fix: don't crash app if flag is present

[DickSmith]

PR Checklist

• The PR title follows our guidelines: https://github.com/NativeScript/NativeScript/blob/master/CONTRIBUTING.md#commit-messages.
• There is an issue for the bug/feature this PR is for. To avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it.
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• All existing tests are passing: https://github.com/NativeScript/ios-runtime/blob/master/CONTRIBUTING.md#contribute-to-the-code-base
• Tests for the changes are included.

What is the current behaviour?

App will crash.

What is the new behaviour?

App will shutdown.

[mbektchiev]

Hi @DickSmith, thank you for the PR! It generally looks good, I'd like you to address the comment and warn you that exiting instead of throwing an exception could mean that automatic exception reporting by Crashlitics could be hindered. The uncaught JS error handler, however, will get called. So if an app has logic for reporting errors there (which is always a good idea), this shouldn't be an issue.

[mbektchiev]

run ci