Ignore git submodule failure in gotorevisionx

gotorevisionx tries to clean up the git repo before checking out a new revision. In b848b99b this was changed to reset and clean any submodule as well. In case upstream has a broken submodule configuration this could fail and we can't checkout the new revision. As we are doing a reset and clean after checking out the new revision anyhow, this change ignores submodule errors before the checkout and only makes sure that the main repo is reset and clean.

This broke checkupdates for apps where old versions had broken submodules. It checkout out the old version and got stuck, not able to checkout any other version.