Don't send PositionChanged messages in TurnTo when not actually turning

FaceTowardsTarget is called quite often by UnitAI, and we can skip some
un-necessary messages as an optimisation.

Differential Revision: https://code.wildfiregames.com/D5005
This was SVN commit r27695.

source/simulation2/components/CCmpPosition.cpp

@@ -556,6 +556,10 @@ public:
 			if (cmpPosition)
 				y -= cmpPosition->GetRotation().Y;
 		}
+		// Don't send messages if we don't actually rotate.
+		if ((y - m_RotY).Absolute() <= fixed::Epsilon())
+			return;
+
 		m_RotY = y;
 
 		AdvertisePositionChanges();