Don't show referrer policy warning if fallback policy set.

Test-Set:

no-referrer-when-downgrade
no-referrer
strict-origin-when-cross-origin
same-origin
no-referrer, strict-origin-when-cross-origin
strict-origin-
unsafe-raw, same-origin
strict-origin-when-downgrade

Signed-off-by: Daniel Kesselberg <mail@danielkesselberg.de>