[6.x] Field margin balance

[jaygeorge]

Description of the Problem

I noticed a couple of issues on the login page with field margins.

• The "Forgot password?" link did not have any bottom margin on it, making it slightly off-balance compared to the Password label (see the red line below)
• There was a blank div slot with mb-2 below it, causing extra margin.

What this PR Does

• Makes sure the slot is not empty before outputting
• Add some margin to the Forgot Password link

You can see the email/password/forgot password labels are correctly balanced now:

How to Reproduce

1. Go to /cp/login