GetURI can succeed, but still return null. In that case, BasePrincipal::IsL10nAllowed
will pass null into NS_URIChainHasFlags, causing it to fail, which will produce three
separate warnings, and then return NS_OK. A recent change caused this function to be
call much more frequently, so this is now the top source of log spam in debug builds.
This change should not affect the behavior, aside from the lack of warnings.
Differential Revision: https://phabricator.services.mozilla.com/D219065
76091b64ec