don't search/replace username in path

fixes faulty URLs when part of the path is used as username (e.g. 'avatars')

lib/routes/avatars.js

@@ -14,7 +14,8 @@ function handle_default(img_status, userId, size, def, req, err, callback) {
       var parsed = req.url;
       delete parsed.query.default;
       delete parsed.search;
-      parsed.pathname = parsed.pathname.replace(userId, def);
+      parsed.path_list[1] = def;
+      parsed.pathname = "/" + parsed.path_list.join("/");
       var newUrl = url.format(parsed);
       callback({
         status: img_status,

lib/routes/renders.js

@@ -19,7 +19,8 @@ function handle_default(rid, scale, overlay, body, img_status, userId, size, def
       var parsed = req.url;
       delete parsed.query.default;
       delete parsed.search;
-      parsed.pathname = parsed.pathname.replace(userId, def);
+      parsed.path_list[2] = def;
+      parsed.pathname = "/" + parsed.path_list.join("/");
       var newUrl = url.format(parsed);
       callback({
         status: img_status,

lib/routes/skins.js

@@ -15,7 +15,8 @@ function handle_default(img_status, userId, def, req, err, callback) {
       var parsed = req.url;
       delete parsed.query.default;
       delete parsed.search;
-      parsed.pathname = parsed.pathname.replace(userId, def);
+      parsed.path_list[1] = def;
+      parsed.pathname = "/" + parsed.path_list.join("/");
       var newUrl = url.format(parsed);
       callback({
         status: img_status,