Add a test for LOG_IN_OR_OUT route and add a missing `^`

Release-Notes: skip
Change-Id: I5ecc40ee13dc238c6e80236a52f391c1c746e142
diff --git a/polygerrit-ui/app/elements/core/gr-router/gr-router.ts b/polygerrit-ui/app/elements/core/gr-router/gr-router.ts
index 88bacdf..e75bc32 100644
--- a/polygerrit-ui/app/elements/core/gr-router/gr-router.ts
+++ b/polygerrit-ui/app/elements/core/gr-router/gr-router.ts
@@ -118,7 +118,9 @@
 
   // Pattern for login and logout URLs intended to be passed-through. May
   // include a return URL.
-  LOG_IN_OR_OUT: /\/log(in|out)(\/(.+))?$/,
+  // TODO: Maybe this pattern and its handler can just be removed, because
+  // passing through is what the default router would eventually do anyway.
+  LOG_IN_OR_OUT: /^\/log(in|out)(\/(.+))?$/,
 
   // Pattern for a catchall route when no other pattern is matched.
   DEFAULT: /.*/,