Reduces unnecessarily thrown exceptions

- when initially loading nodes and relationships, i.e. mostly checking
  that such exists. Previously went through a path throwing
  InvalidRecordException. Now uses method returning null or record.
- when visiting node degrees for state before commit, as part of
  committing nodes. Previously went through path throwing
  EntityNotFoundException. Now uses method returning boolean.
Merge pull request #3563 from tinwelint/2.2-less-thrown-exceptions

Reduces unnecessarily thrown exceptions