Client: assume uid==0 is local socket

A negative uid value means it's not a "local socket" (PF_LOCAL).
uid==0 means user "root" connected.

src/Client.hxx

@@ -109,7 +109,7 @@ public:
 	 * a local (UNIX domain) socket?
 	 */
 	bool IsLocal() const {
-		return uid > 0;
+		return uid >= 0;
 	}
 
 	unsigned GetPermission() const {