zip::walk fails with sub-directories which names start with '-', due to missing '--' in glob expressions.<p>

Can be reproduced like this:
<pre>
$ mkdir -- -1
$ ls
-1/
$ tclsh
% package require Tcl 8.6
8.6.7
% package require zipfile::mkzip
1.2
% ::zipfile::mkzip::mkzip my.zip -directory .
bad option "-1/*": must be -directory, -join, -nocomplain, -path, -tails, -types, or --
</pre>

Please consider applying the attached patch with a fix.<p>

Regards,<br/>
Héctor Romojaro