R1:45fc4f6f6407

Iterate over ranges correctly for encryped files

Summary:
Fixes T12079. Currently, when a file is encrypted and a request has "Content-Range", we apply the range first, //then// decrypt the result. This doesn't work since you can't start decrypting something from somewhere in the middle (at least, not with our cipher selection).

Instead: decrypt the result, //then// apply the range.

Test Plan: Added failing unit tests, made them pass

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T12079…