[gameplay] Heimer's turrets don't transition from attacking tower to inhib

When playing as Heimerdinger, your turrets don't switch from attacking the tower when it's destroyed to attacking the inhibitor. Instead, they sit there as if there is no target within range until they're killed. It is not an issue of range; a turret placed directly between the tower and inhib, and clearly within range of the inhib, acts exactly the same way.

TL;DR Heimer's existing turrets don't identify the inhibitor as a target when the inhib tower is destroyed.