Fixed fields missing the readonly modifier

OpenRA.Mods.Common/Activities/Move/Drag.cs

@@ -21,10 +21,11 @@ namespace OpenRA.Mods.Common.Activities
 	{
 		readonly IPositionable positionable;
 		readonly IDisabledTrait disableable;
-		WPos start, end;
-		int length;
+		readonly WPos start;
+		readonly WPos end;
+		readonly int length;
 		int ticks = 0;
-		WAngle? desiredFacing;
+		readonly WAngle? desiredFacing;
 
 		public Drag(Actor self, WPos start, WPos end, int length, WAngle? facing = null)
 		{

OpenRA.Mods.Common/Activities/Move/Move.cs

@@ -49,7 +49,7 @@ namespace OpenRA.Mods.Common.Activities
 		int waitTicksRemaining;
 
 		// To work around queued activity issues while minimizing changes to legacy behaviour
-		bool evaluateNearestMovableCell;
+		readonly bool evaluateNearestMovableCell;
 
 		// Scriptable move order
 		// Ignores lane bias and nearby units

OpenRA.Mods.Common/Activities/Move/MoveAdjacentTo.cs

@@ -111,7 +111,7 @@ namespace OpenRA.Mods.Common.Activities
 			return TickChild(self);
 		}
 
-		List<CPos> searchCells = new List<CPos>();
+		readonly List<CPos> searchCells = new List<CPos>();
 		int searchCellsTick = -1;
 
 		List<CPos> CalculatePathToTarget(Actor self, BlockedByActor check)