Fix segfault

src/lib/Configuration.vala

@@ -17,7 +17,7 @@ namespace Usm {
                     .when_undefined(o => o.managed_config = null);
                 cfg.map_properties_with<Paths>("paths", o => o.paths, (o, v) => o.paths = v, Paths.get_mapper())
                     .undefined_when(o => o.paths == null)
-                    .when_undefined(o => new Paths.usm_environ());
+                    .when_undefined(o => o.paths = new Paths.usm_environ());
                 cfg.set_constructor(() => new Configuration());
             });
         }