http-push: clean up loose request when falling back to packed

In http-push's finish_request(), if we fail a loose object request we may fall back to trying a packed request. But if we do so, we leave the http_loose_object_request in place, leaking it. We can fix this by always cleaning it up. Note that the obj_req pointer here (which we'll set to NULL) is a copy of the request->userData pointer, which will now point to freed memory. But that's OK. We'll either release the parent request struct entirely, or we'll convert it into a packed request, which will overwrite userData itself. This leak is found by t5540, but it's not quite leak-free yet. Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>