Initializing a relation can result in the loss of pending changes

[followben]

Describe the bug
Lazily populating a bidirectional relation inadvertently writes any pending changes for the parent (and any onward relations) to the EntityManager's originalEntityData map. When the resulting UnitOfWork is committed, those changes are omitted from the changeSet and never written to the DB.

To Reproduce
Steps to reproduce the behavior:

1. Fetch an entity instance but don't populate any bidirectional relations
2. Change a property on the fetched instance (e.g. a scalar value)
3. Initialize a bidirectional relation and change it (e.g. add a new instance to a Collection)
4. Call em.persistAndFlush()

Expected behavior
Both changes are persisted to the database.

Actual behavior
Only the 2nd change, after the relation init(), is persisted.

Versions

Dependency	Version
node	13.10.1
typescript	3.8.3
mikro-orm	3.6.7
pg	7.18.2

[B4nan]

Thanks for the repro, appreciated!