one-to-many with composite key can throw OutOfBoundsException

[croensch]

This is a follow up to #298 please take a look at the comment there too.

I have a one-to-many mapping in which the association table has a composite key simply of both keys right and left of the association. Now if i try to load the entity with a join it will try to hydrate the associations too. It has half of the key so it will pass it to AbstractProxyFactory, but that will now throw an OutOfBoundsException.

The same data worked flawless with 2.3.x

[croensch]

I was looking at the wrong association in our production code. There was another wich was faulty, or better the data thereof. I could NOT reproduce it here: croensch/doctrine2-orm-tutorial@f4d7c3c

So i think the exception is fine.