Avoid doing anything on HDFSBackedStateStore.abort() when there are no updates to commit

During Streaming Aggregation, we have two StateStores per task, one used as read-only in StateStoreRestoreExec, and one read-write used in `StateStoreSaveExec`. `StateStore.abort` will be called for these StateStores if they haven't committed their results. We need to make sure that abort in read-only store after a commit in the read-write store doesn't
accidentally lead to the deletion of state.

This JIRA proposes a test for this case. StateStore implementations should successfully handle this use case.