CLEANUP: http: remove a useless null check

CLEANUP: http: remove a useless null check

srv cannot be null in http_perform_server_redirect(), as it's taken
from the stream interface's target which is always valid for a
server-based redirect, and it was already dereferenced above, so in
practice, gcc already removes the test anyway.

Reported-by: Dinko Korunic <dkorunic@reflected.net>