empty path input corrupts svnauthz => trac aborts

#6265 was closed as a duplicate.

I made a Q&D solution to solve this problem : edit the "admin_ui.py" file and in the method "_add_path" just before the "try" add the following lines :

if not path :
    return {}

Finally the method looks like this :

    def _add_path(self, req):
        path = req.args.get('path')
        repository = None
        tmppath = req.args.get('path') 
 	if ":" in tmppath: 
 	    repository, path = tmppath.split(":") 
 	    repository = repository.strip() 
 	    path = path.strip() 
 	else: 
 	    repository = self.authz_module 
 	    path = tmppath.strip() 
        if not path :
            return {}
        try:
            self.authz.add_path(Path(path, [], repository))
	    return {}
        except Exception, e:
            return {'addpath_error' :  e}

(In [11873]) Fixes #5689:

• Added checks for non-empty group and path before attempting to add them. A warning is added if either are empty.
• Extracted code to a method _get_authz.
• Corrected tabs and indentation.