don't apply invalid ordering when preloading hmt associations.

closes #8663.

When preloading a hmt association there two possible scenarios:

1.) preload with 2 queries: first hm association, then hmt with id IN ()
2.) preload with join: hmt association is loaded with a join on the hm association

The bug was happening in scenario 1.) with a normal order clause on the hmt association.
The ordering was also applied when loading the hm association, which resulted in the error.

This patch only applies the ordering the the hm-relation if we are performing a join (2).
Otherwise the order will only appear in the second query (1).