Fixes invalid battle state

PkmnLib.Dynamic/Models/BattleSide.cs

@@ -133,6 +133,10 @@ public class BattleSideImpl : ScriptSource, IBattleSide
         _pokemon = new IPokemon?[numberOfPositions];
         _setChoices = new ITurnChoice?[numberOfPositions];
         _fillablePositions = new bool[numberOfPositions];
+        for (byte i = 0; i < numberOfPositions; i++)
+        {
+            _fillablePositions[i] = true;
+        }
         Battle = battle;
         VolatileScripts = new ScriptSet();
     }