[gcmd-dev] fix for smb browsing crash

[koos]

Hello Piotr,

Here is a fix for a crash when browsing smb shares.
To reproduce the crash one need to do the following steps.
1. go to smb
2. enter a 'workgroup'
3. enter a smb-server
4. click on the 'history arrow' that sits right above the file-list and
select the smb-server

The cause of this crash was a malformed gnomecmdpath
(e.g. //SERVER/(null) ). This patch makes sure that the gnomecmdpath is
valid. 
I hope the solution is a sensible one as the creating the directory
listings is rather complicated in my opinion. A lot of functions are
involved in this process.
Furthermore I noticed there is a inconsistancy in the smb directory
listings. When one enters a smb-server (like step 2) the parent-dir
(the two dots) is shown. When browsing through a couple of other
directories and returning to this point the parent-dir is not shown.

koos