Fix new dropdown showing on mobile with no items

What does this MR do?

This MR fixes an issue where the new dropdown rendered in the mobile view would show up, even though there were not any menu items.

Screenshots (strongly suggested)

How to test:

Setup:

1. As an Admin, create a new user and make sure it is set to "External" and cannot create any projects
2. Impersonate this user
3. Shrink the screen size to trigger the mobile nav
4. Click "Menu"

Expected (this MR):

1. The "+" nav shouldn't show up 🎉.

Actual (on master):

1. The "+" nav shows up, and when clicked, shows an empty white box.

Before (on master after clicking "+")	After (this MR)

Does this MR meet the acceptance criteria?

Conformity

• [ ] I have included changelog trailers, or none are needed. (Does this MR need a changelog?) Not needed since feature is behind a feature flag
• I have added/updated documentation, or it's not needed. (Is documentation required?)
• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• I have added information for database reviewers in the MR description, or it's not needed. (Does this MR have database related changes?)
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.
• This change is backwards compatible across updates, or this does not apply.

Availability and Testing

• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)
• I have tested this MR in all supported browsers, or it's not needed.