pidgin/pidgin

Fix up the XEP-0280 carbons support.

2021-01-30, Gary Kramlich
2fc55152b79c
Fix up the XEP-0280 carbons support.

My initial port of this wasn't great, this is much better.

Testing Done:
sent messages between pidgin2 with gkdr/carbons, conversations on my phone, and pidgin3. I sent messages from all clients and received them on all three clients.

Reviewed at https://reviews.imfreedom.org/r/462/
libpurple/data/purple-url-handler.desktop.in
libpurple/protocols/null/nullprpl.c
pidgin/data/im.pidgin.Pidgin.desktop.in
sub/libpurple/data/purple-url-handler.desktop.in
sub/libpurple/protocols/null/nullprpl.c
sub/pidgin/data/im.pidgin.Pidgin.desktop.in