404 error when creating new branch in web interface with pull requests disabled

[bmerrison]

• Gitea version (or commit ref): 1.9.3 built with GNU Make 4.1, go1.12.9 : bindata, sqlite, sqlite_unlock_notify
• Git version: 2.1.4
• Operating system: Debian Jessie
• Database (use [x]):
  • PostgreSQL
  • MySQL
  • MSSQL
  • SQLite
• Can you reproduce the bug at https://try.gitea.io:
  • Yes (not sure how to provide URL as you'd need to be added to my repo)
  • No
  • Not relevant

Description

Working Case:

1. Ensure Pull Requests are enabled in a repository's settings.
2. Manually edit a file using the web GUI. Choose to commit the change onto a new branch.
3. The change is committed successfully onto a new branch.

Not-working Case:

1. Ensure Pull Requests are disabled in a repository's settings.
2. Manually edit a file using the web GUI. Choose to commit the change onto a new branch.
3. The change is committed successfully onto a new branch but the page returns a 404:

This has only become an issue since upgrading from 1.8.0 to 1.9.3.