Fixed duplication of Model's afterFind callback in HABTM relation [ticket 3970]

It is my first time with git and sorry if I did something wrong. 

This changes fixes duplication of afterFind callback on Model related with HABTM. It's related to ticket #995 like i wrote in my ticket. Changes are simple - just copy and paste function flow from processing hasMany relation data. 

I didn't make any test case but ModelTests all passed
310/319 test methods complete: 310 passes, 0 fails, 1478 assertions and 0 exceptions.