To reproduce:

1. Download and open attached "BugReport.zip" project.
2. Open "Scene" scene.
3. Enter Play mode.
4. Press A on keyboard to trigger animation.
5. Notice the console window.

Expected result: Console throws more descriptive warning. Since Animator does have a controller and it is only disabled, it should say that object with the animator is disabled or some other more descriptive information.
Actual result: Console throws irrelevant warning. It says that "Animator does not have an AnimatorController" when in fact it does have one, simply the object is disabled.

Reproduced with: 2017.3.0a7, 2017.2.0b10, 2017.1.1f1, 5.6.3p2, 5.5.4p4.