Reset possible helper before reusing remote structure

Reset possible helper before reusing remote structure

If one had multiple URLs configured for remote with previous one
having forced helper but the subsequent one not, like:

url = foo::bar://baz
url = ssh://example/example.git

Then the subsequent URL is passed to foo helper, which isn't
correct. Fix it to be parsed normally by resetting foreign VCS
name before parsing the URL protocol.

Signed-off-by: Ilari Liusvaara <ilari.liusvaara@elisanet.fi>
Signed-off-by: Junio C Hamano <gitster@pobox.com>