realpath invokation on the media directory requires read access to all parent directories

[obadz]

chdir (executable) access should be sufficient for all directories leading up to the media dir itself.

The problematic line is: https://github.com/azatoth/minidlna/blob/master/minidlna.c#L475

Other invokations of realpath follow this pattern:

				path = realpath(x, y);
				if( !path )
					path = x

… which tackles the issue and we should probably follow here as well?