Clear stale special action before assigning battle node action

Battle nodes may be reused or updated without receiving a new special action
from the destination node. Reset specialAction first so stale actions from a
previous node state are not accidentally preserved.

This keeps generated battle paths from executing unrelated special actions.

AI/Nullkiller2/Pathfinding/Rules/AIMovementAfterDestinationRule.cpp

@@ -331,6 +331,8 @@ namespace AIPathfinding
 
 		if(loss < actualArmyValue)
 		{
+			battleNode->specialAction = nullptr;
+
 			if(destNode->specialAction)
 			{
 				battleNode->specialAction = destNode->specialAction;