FBB: More lenient date\time parsing

[xylo04]

There's a bug report on the BPQ forum: https://groups.io/g/bpq32/message/35117. I don't know what the spec says about the date\time format, but BPQ evidently uses a different format than other RMS's.

MID: 7975_W7WXV
Date: 20220513002343 <<<< generated from BPQ web browser, blows up PAT clients
Type: Bulletin
From: W7WXV
To: kg7av
Subject: test 3
Mbo: W7WXV
Body: 56
File: 194 or-wxv-22-014.k2s

vs

Date: 2022/05/13 00:27 <<<< generated from RMS Express, all clients handle this fine

[martinhpedersen]

Ah, yet another date format for the FBB Date header then 🤣

The "spec" merely gives an example string of 1999/09/22 14:33.

We already support lots of formats, but let's add this one to the list of explicit winlink formats. 👍

[martinhpedersen]

Btw, should we verify that this is in UTC? 🤔

[martinhpedersen]

This is how Winlink describes the Date header:

The Date: field is the UTC date and time the message was originated and is in the format YYYY/MM/DD HH:MM.