icecast: information leak

It was reported that Icecast could possibly leak the contents of
on-connect scripts to clients, which may contain sensitive information.

If on-connect/on-disconnect scripts are used, file descriptors of the
server process remain open and could be written to or read from. Most
pressing STDIN, STDOUT, STDERR are handled.
Further all file descriptors up to 1024 are closed. There is a remaining
(much lower) risk in combination of either a malicious or susceptible
script and FDs above 1024.