Regression: Fix file uploads

The change introduced in Iadb4ee2b336e07ae2dfec7f09798ba210f409f6b
prevents uploads from having format=json set. This rectifies that.

Change-Id: I5ac0f7aa26f28841ad1a2c1a9cca07d0e5f8a2c0
(cherry picked from commit 819e673624489041ddffa4816535735b6e65804e)