hangs when pasting URL from clipboard

[Moses Moore]

Pidgin hangs when pasting http:// or https:// URLs into the text entry field. Can't kill it, must kill -9 the process.

Steps to reproduce:
- open chat window to a jabber/xmpp contact
- type "http://www.launchpad.net/" in a separate terminal window. highlight with the mouse, Ctrl-C to copy.
- focus on chat window, Ctrl-V paste

What I expect:
 The text appears in the chat window, and the chat window still response to keyboard/mouse input.

What I see:
 Text does not appear, pidgin stops responding to any input, maybe even stops updating its windows.

Other info:
Doesn't hang if I use `xclip -selection clipboard -i <<<"https://www.launchpad.net"` then Ctrl-V to paste.

Saw this in the `pidgin -d` debug logs:

```
(18:50:23) jabber: Sending (ssl) (<email address hidden>/HomeXXXXXXXX): <message type='chat' id='purple7bf2509b' <email address hidden>'><composing xmlns='http://jabber.org/protocol/chatstates'/></message>
(18:50:29) Gtk: Failed to set text from markup due to error parsing markup: Attribute 'fontdesc' is not allowed on the <span> tag on line 1 char 39
(18:50:29) Gtk: Failed to set text from markup due to error parsing markup: Attribute 'fontdesc' is not allowed on the <span> tag on line 1 char 39
(18:50:29) Gtk: Failed to set text from markup due to error parsing markup: Attribute 'fontdesc' is not allowed on the <span> tag on line 1 char 39
dns[1116855]: nobody needs me... =(
```

Might be Gtk misbehaving with clipboard data, and pidgin goes catatonic dealing with a bad message from Gtk?

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: pidgin 1:2.13.0-2.2ubuntu4
ProcVersionSignature: Ubuntu 5.4.0-26.30-generic 5.4.30
Uname: Linux 5.4.0-26-generic x86_64
NonfreeKernelModules: nvidia_modeset nvidia
ApportVersion: 2.20.11-0ubuntu27
Architecture: amd64
CasperMD5CheckResult: skip
CurrentDesktop: XFCE
Date: Thu May 14 18:51:18 2020
InstallationDate: Installed on 2016-06-05 (1439 days ago)
InstallationMedia: Xubuntu 16.04 LTS "Xenial Xerus" - Release amd64 (20160420.1)
SourcePackage: pidgin
UpgradeStatus: Upgraded to focal on 2020-04-25 (19 days ago)
modified.conffile..etc.default.apport: [modified]
mtime.conffile..etc.default.apport: 2018-03-20T22:16:27.108498

[Birgit Edel (biredel)]

Possible duplicate LP: #1975519