Setting null to counter should be a no-op (#11012)

core/src/mindustry/logic/LVar.java

@@ -103,9 +103,13 @@ public class LVar{
 
     public void set(LVar other){
         isobj = other.isobj;
+        // Setting a non-numeric value to @counter must preserve its numeric field
+        if(isobj){
             objval = other.objval;
+        }else{
             numval = other.numval;
         }
+    }
 
     public static boolean invalid(double d){
         return Double.isNaN(d) || Double.isInfinite(d);