Checkout branch should quit early if uncommitted changes detected.

When checking out an existing branch, if there are uncommitted changes, then git will not complete the checkout. However, the pull handler will still proceed with refreshing Iris based on the `git diff`, which is now inaccurate (because it can potentially try to load classes that don't exist in the checkout)

The change needs to take place somewhere within `RunGitCommandWithInput()` before `SyncIrisWithRepoThroughDiff()` is called. I think I have a solution, but I need to run a few more tests first.

Inizia da RunGitCommandWithInput() e traccia il percorso fino a SyncIrisWithRepoThroughDiff() durante il checkout di un branch esistente. Conferma il comportamento quando modifiche non committate impediscono git checkout, quindi assicurati che l’handler del pull non continui ad aggiornare Iris a partire dal git diff non accurato.

Scritto dal modello di indicizzazione a partire dal testo della issue.