smart transport: only clear url on hard reset

After creating a transport for a server, we expect to be able to call
`connect`, then invoke subsequent `action` calls.  We provide the URL to
these `action` calls, although our built-in transports happen to ignore
it since they've already parsed it into an internal format that they
intend to use (`gitno_connection_data`).

In ca2eb460, we began clearing the URL
field after a connection, meaning that subsequent calls to transport
`action` callbacks would get a NULL URL, which went undetected since the
builtin transports ignore the URL when they're already connected
(instead of re-parsing it into an internal format).

Downstream custom transport implementations (eg, LibGit2Sharp) did
notice this change, however.

Since `reset_stream` is called even when we're not closing the
subtransport, update to only clear the URL when we're closing the
subtransport.  This ensures that `action` calls will get the correct URL
information even after a connection.

src/transports/smart.c

@@ -45,14 +45,13 @@ GIT_INLINE(int) git_smart__reset_stream(transport_smart *t, bool close_subtransp
 		t->current_stream = NULL;
 	}
 
-	if (t->url) {
+	if (close_subtransport) {
 		git__free(t->url);
 		t->url = NULL;
-	}
 
-	if (close_subtransport &&
-		t->wrapped->close(t->wrapped) < 0)
-		return -1;
+		if (t->wrapped->close(t->wrapped) < 0)
+			return -1;
+	}
 
 	return 0;
 }