Calendar crash if date format be writen in non-latin digit

Steps to reproduce

1. Set mobile phone language to Persian
2. Make some event in desirable calendar and sync with NextCloud
3. Now issue is visible. Sync wont happen anymore, calendar on Nextcloud gets corrupted and wont work anymore.

Expected behaviour

It should work as usual!

Actual behaviour

Actually, when language on Android is set to Persian, datetime chages from lating digits to Persian digits (datetime remains same but digits gets replaced). It seems Nextcloud calendar cannot handle such format. The solution is simple: convert digits to Latin on import/sync.

Calendar app

Calendar app version: (see apps admin page, e.g. 2.0.1)

CalDAV-clients used: (Thunderbird Lightning, DAVx5, Evolution, macOS Calendar, etc)
DAVx5

Client configuration

Browser: (e.g. Firefox 48)
doesn't matter.

Operating system: (e.g. Arch Linux)
doesn't matter.

Server configuration

doesn't matter.

Operating system: (e.g. Debian 8)
doesn't matter.

Web server: (e.g. Apache, Nginx,...)
doesn't matter.

Database: (e.g. MariaDB, SQLite or PostgreSQL)
doesn't matter.

PHP version: (e.g. 7.0.3)
doesn't matter.

Nextcloud Version: (see admin page, e.g. 17.0.2)
doesn't matter.

Updated from an older installed version or fresh install:
both
List of activated apps:
not relevant

Reproduce the failure with a Persian-language Android phone, a synced calendar, and DAVx5, then trace the calendar import or sync path. Done means Persian digits no longer corrupt the Nextcloud calendar and synchronization continues normally.