Add a check to register route handler

Change-Id: I59d465eb155b7e6fbf5cf739e2cd03c266f8f6e3
diff --git a/polygerrit-ui/app/elements/core/gr-router/gr-router.js b/polygerrit-ui/app/elements/core/gr-router/gr-router.js
index 7675670..ee45d50 100644
--- a/polygerrit-ui/app/elements/core/gr-router/gr-router.js
+++ b/polygerrit-ui/app/elements/core/gr-router/gr-router.js
@@ -348,6 +348,7 @@
     page(/^\/register(\/.*)?/, ctx => {
       app.params = {justRegistered: true};
       const path = ctx.params[0] || '/';
+      if (path[0] !== '/') { return; }
       page.show(path);
     });