FIX: handle timezone detection errors (PR #3095)

Fixes https://meta.discourse.org/t/importer-for-simple-machines-2-forums/17656/51?u=elberet and provides a means to specify the timezone if PHP isn’t installed.

GitHub

You’ve signed the CLA, Elberet. Thank you! This pull request is ready for review.

Looks fine to me. Thanks :+1: