Segfault when unloading a script that registers for 'script destroyed' signals

[Stevie-O]

Script unloading is done in the wrong order:

1. Destroy the Perl package for the script
2. Emit 'signal destroyed' signal
3. Unhook signal handlers for the script

If a script adds a 'script destroyed' signal handler, unloading the script will cause step 2 to attempt to invoke the 'signal destroyed' handler in the script (because the signal handlers aren't yet removed). However, because the Perl package has been destroyed, this will cause a script error, which will in turn attempt to unload the script (again). This will continue recursively until either stack or heap space is exhausted and the program segfaults.

To reproduce, simply load this script, then unload it:

use strict;
use Irssi qw/signal_add signal_register active_win/;
use Data::Dumper;

signal_register({ 'script error' => [ 'Irssi::Script', 'string' ] });
signal_register({ 'script created' => [ 'Irssi::Script' ] });
signal_register({ 'script destroyed' => [ 'Irssi::Script' ] });

sub scriptevent {
eval {
	active_win->command("SAY ScriptEvent: ($_[0]) $_[1]{package}");
};
}

signal_add('script error', sub { scriptevent('script error', $_[0]); });
signal_add('script created', sub { scriptevent('script created', $_[0]); });
signal_add('script destroyed', sub { scriptevent('script destroyed', $_[0]); });

[Stevie-O]

I have created a pull request with the fix: 661