Fix bug which caused exceptions when attempting to redirect to the console login page

When the registrar console code determines that a user has not logged in, it redirects to a login page. But when authenticating as an internal request (which should never happen), the redirection code encountered an exception, resulting in a 500 error.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=163867018

java/google/registry/ui/server/registrar/ConsoleUiAction.java

@@ -82,7 +82,19 @@ public final class ConsoleUiAction implements Runnable {
   public void run() {
     if (!authResult.userAuthInfo().isPresent()) {
       response.setStatus(SC_MOVED_TEMPORARILY);
-      response.setHeader(LOCATION, userService.createLoginURL(req.getRequestURI()));
+      String location;
+      try {
+        location = userService.createLoginURL(req.getRequestURI());
+      } catch (IllegalArgumentException e) {
+        // UserServiceImpl.createLoginURL() throws IllegalArgumentException if underlying API call
+        // returns an error code of NOT_ALLOWED. createLoginURL() assumes that the error is caused
+        // by an invalid URL. But in fact, the error can also occur if UserService doesn't have any
+        // user information, which happens when the request has been authenticated as internal. In
+        // this case, we want to avoid dying before we can send the redirect, so just redirect to
+        // the root path.
+        location = "/";
+      }
+      response.setHeader(LOCATION, location);
       return;
     }
     User user = authResult.userAuthInfo().get().user();