Core/Movement: Prevent IdleMovementGenerator being put into MOTION_SLOT_IDLE and MOTION_SLOT_ACTIVE simultaneously

src/server/game/Movement/MotionMaster.cpp

@@ -175,12 +175,11 @@ void MotionMaster::DelayedExpire()
         --i_top;
 }
 
-void MotionMaster::MoveIdle(MovementSlot slot)
+void MotionMaster::MoveIdle()
 {
-    //if (empty() || !isStatic(top()))
-    //    push(&si_idleMovement);
-    if (!isStatic(Impl[slot]))
-        Mutate(&si_idleMovement, slot);
+    //! Should be preceded by MovementExpired or Clear if there's an overlying movementgenerator active
+    if (empty() || !isStatic(top()))
+        Mutate(&si_idleMovement, MOTION_SLOT_IDLE);
 }
 
 void MotionMaster::MoveRandom(float spawndist)

src/server/game/Movement/MotionMaster.h

@@ -142,7 +142,7 @@ class MotionMaster //: private std::stack<MovementGenerator *>
                 DirectExpire(reset);
         }
 
-        void MoveIdle(MovementSlot slot = MOTION_SLOT_ACTIVE);
+        void MoveIdle();
         void MoveTargetedHome();
         void MoveRandom(float spawndist = 0.0f);
         void MoveFollow(Unit* target, float dist, float angle, MovementSlot slot = MOTION_SLOT_ACTIVE);