Bug#868686: ring: Doesn't register to SIP account with username containing "@"

[Limewood]

Hello,

I have a SIP account provided by the VoIP provider Worldcall and the SIP
username is the e-mail address used for creating the account. The SIP
username therefore contains the "@" sign. This SIP account works well
withthe Twinkle softphone, so it looks like a sip account name can
contain an at sign.