Anonymous user unable to fill in email field when email address is required

When Bugherd is open for anonymous users to submit feedback and the email address is required, the email address field in the Bugherd popup cannot be modified because it is always being set to an empty value. I had to change the code so that the email portion of the bugherdconfig variable is added conditionally.

Steps to reproduce:

1. In Bugherd settings, set email address to required
2. Set the "access bugherd" permission for anonymous users
3. View the site as an anonymous user
4. Click "Send feedback", choose either feedback option
5. Attempt to click into the "Your email address field" but it is not possible because it is disabled