Setting NO_CURL leaves some variables like REMOTE_CURL_ALIASES
empty, which creates no fun when for-looping over
$(REMOTE_CURL_ALIASES) unconditionally. Make it conditional.
Reported-by: Paul Walker <PWalker752@aol.com> Signed-off-by: Michael J Gruber <git@drmicha.warpmail.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>