[ResourceBundle] Prevent overriding existing association mappings

[vntw]

Q	A
Bug fix?	yes
New feature?	no
BC breaks?	no
License	MIT

If the metadata already has existing association mappings for the given field, we won't override anything and leave it as is.

Example:
In our bundle, we define our own product entity and want to add an order-by to the association mapping of an existing field. So we copy the field definition from Product.orm.xml to our own configuration and modify it to our needs.

The current code will always override our custom association mappings for a given field. So the fix is to check if the field has custom association mappings and only apply them if none are configured.

Also renamed the hasRelation method since it's really checking if it is a relation.

[pjedrzejewski]

Thanks @venyii, this is a great improvement! :)