some CardDav servers put "\," into vCard downloads of attributes

[derwok]

TL;DR: Pull request in preparation.

Some CardDav servers - e.g., Baikal (sabre/dav) - sends a attribute with embedded comma (,) in XML with "\,". The quote backslash survives all our processing chain right into the Fritz!Box upload.

Example: Display in CardDav-Editor:

Example: Display in Fritz!Box Browser UI:

Root cause is the specified BACKSLASH quoting of COMMA, SEMICOLON & BACKSLASH described in the vCard standard:
https://tools.ietf.org/html/rfc6350#section-3.4

As a consequence, FritzFon displays ugly "\" in some contacts names. And even breaks Phone numbers with comma. (A comma in a phone number is a pause!)

Solution: replace \{SPECIALCHAR} => {SPECIALCHAR} in values in the vCard parser