protondrive: restore the config storage even when rclone's config is in memory

The password test's cleanup restored the config path before the
storage, and setting the storage does nothing while the path is empty,
so with an in-memory config the storage was left behind.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

backend/protondrive/security_test.go

@@ -688,9 +688,10 @@ func TestPasswordStoredObscured(t *testing.T) {
 	path := filepath.Join(t.TempDir(), "rclone.conf")
 	require.NoError(t, config.SetConfigPath(path))
 	t.Cleanup(func() {
-		assert.NoError(t, config.SetConfigPath(oldPath))
+		// SetData does nothing without a config path.
 		config.SetData(oldData)
 		assert.True(t, config.Data() == oldData, "the config storage isn't restored")
+		assert.NoError(t, config.SetConfigPath(oldPath))
 	})
 	configfile.Install()