remote: don't free transport on disconnect

Currently, git_remote_disconnect not only closes the connection but also
frees the underlying transport object, making it impossible to write
code like

	// fetch stuff
	git_remote_download()

	// close connection
	git_remote_disconnect()

	// call user provided callback for each ref
	git_remote_update_tips(remote, callback)

because remote->refs points to references owned by the transport object.
This means, we have an idling connection while running the callback for
each reference.

Instead, allow immediate disconnect and free the transport later in
git_remote_free().

examples/network/fetch.c

@@ -93,6 +93,9 @@ int fetch(git_repository *repo, int argc, char **argv)
   } while (!data.finished);
   printf("\rReceived %d/%d objects in %d bytes\n", stats.processed, stats.total, bytes);
 
+  // Disconnect the underlying connection to prevent from idling.
+  git_remote_disconnect(remote);
+
   // Update the references in the remote's namespace to point to the
   // right commits. This may be needed even if there was no packfile
   // to download, which can happen e.g. when the branches have been

src/remote.c

@@ -381,13 +381,8 @@ void git_remote_disconnect(git_remote *remote)
 {
 	assert(remote);
 
-	if (remote->transport != NULL) {
-		if (remote->transport->connected)
+	if (remote->transport != NULL && remote->transport->connected)
 			remote->transport->close(remote->transport);
-
-		remote->transport->free(remote->transport);
-		remote->transport = NULL;
-	}
 }
 
 void git_remote_free(git_remote *remote)
@@ -395,14 +390,21 @@ void git_remote_free(git_remote *remote)
 	if (remote == NULL)
 		return;
 
+	if (remote->transport != NULL) {
+		git_remote_disconnect(remote);
+
+		remote->transport->free(remote->transport);
+		remote->transport = NULL;
+	}
+
+	git_vector_free(&remote->refs);
+
 	git__free(remote->fetch.src);
 	git__free(remote->fetch.dst);
 	git__free(remote->push.src);
 	git__free(remote->push.dst);
 	git__free(remote->url);
 	git__free(remote->name);
-	git_vector_free(&remote->refs);
-	git_remote_disconnect(remote);
 	git__free(remote);
 }