Binary files without changes are shown when using keyboard nav `n` and `p`

[ioanarusiczki]

trafficstars

Followup for https://github.com/mozilla/addons-code-manager/issues/914 STR:

1. Load dev and go to https://code.addons-dev.allizom.org/en-US/compare/616913/versions/1688316...1688317/?path=META-INF%2Fmanifest.mf#D5 or any other compare view for an add-on with changes
2. Use the n to go forward to the next change

Expected result: Only the changed lines are shown.

Actual result: Files with no changes (in this case the cose.sig or mozilla.rsa are shown).

Notes: This is reproducible on -dev with FF68(win10).

┆Issue is synchronized with this Jira Task

[kumar303]

@bobsilverberg hmm, I'm not sure what we should do here since it's a binary file, for which we don't display content