Use-after-free bug after reopening connection

Hello,

There have recently been some issues when using libshout in combination with MPD (the Music Player Daemon) which, after some investigation in collaboration with the author of MPD, have apparently been tracked to a bug in libshout. MPD's author reported the issue but did so on your GitHub mirror, so in case you may have missed it I saw fit to report it here as well.

The gist of that bug report is as follows:

"Since libshout 2.4.2, the library crashes due to a use-after-free and double-free bug if an application reopens the connection using shout_open() after a previous connection with the same shout_t had been closed by shout_close(). See MusicPlayerDaemon/MPD#622 for details and valgrind logs. The crash bug was introduced by commit 3110fe32"

The original bug report is here: xiph/Icecast-libshout#17