fix(manifest): correct resource install path handling

src/lib/Manifest.vala

@@ -399,7 +399,9 @@ namespace Usm {
                             if(install_path == null) {
                                 throw new ManifestError.INVALID_FILE_PATH("Install path was not provided");
                             }
-                            base_path = Path.build_filename(install_path, paths.get_suggested_path_for_resource(resource.key));
+                            var install_paths = paths.clone();
+                            install_paths.destination = install_path;
+                            base_path = paths.get_suggested_path_for_resource(resource.key);
                             break;
                         default:
                             assert_not_reached();