fix($http): don't covert 0 status codes to 404 for non-file protocols

PR #5547 introduced conversion of all 0 status codes to 404 for cases
where no response was recieved (previously this was done for the
file:// protocol only). But this mechanism is too eager and
masks legitimate cases where status 0 should be returned. This commits
reverts to the previous mechanism of handling 0 status code for the
file:// protocol (converting 0 to 404) while retaining the returned
status code 0 for all the protocols other than file://

Fixes #6074
Fixes #6155