[Qt] properly copy IPv6 externalip MN info
[Qt] properly copy IPv6 externalip MN info

IPv6 addresses use `:` rather than `.` characters in their notation,
so needed to change the way `externalip` was being copied here.

PIVX-Project/PIVX,PIVX-Project/PIVX,Mrs-X/Darknet,Darknet-Crypto/Darknet,Mrs-X/PIVX,Darknet-Crypto/Darknet,Mrs-X/Darknet,PIVX-Project/PIVX,Mrs-X/PIVX,Darknet-Crypto/Darknet,Mrs-X/Darknet,PIVX-Project/PIVX,PIVX-Project/PIVX,PIVX-Project/PIVX,Mrs-X/PIVX,Mrs-X/Darknet,PIVX-Project/PIVX,Mrs-X/PIVX,Darknet-Crypto/Darknet,Mrs-X/PIVX,Darknet-Crypto/Darknet,Mrs-X/Darknet,Darknet-Crypto/Darknet,PIVX-Project/PIVX,Mrs-X/Darknet,Mrs-X/PIVX,PIVX-Project/PIVX