Fix C# mistakes in Custom drawing in 2D

Fixes #5107

tutorials/2d/custom_drawing_in_2d.rst

@@ -183,16 +183,18 @@ In our example, we will simply use a fixed number of points, no matter the radiu
     public void DrawCircleArc(Vector2 center, float radius, float angleFrom, float angleTo, Color color)
     {
         int nbPoints = 32;
-        var pointsArc = new Vector2[nbPoints];
+        var pointsArc = new Vector2[nbPoints + 1];
 
-        for (int i = 0; i < nbPoints; ++i)
+        for (int i = 0; i <= nbPoints; i++)
         {
             float anglePoint = Mathf.Deg2Rad(angleFrom + i * (angleTo - angleFrom) / nbPoints - 90f);
             pointsArc[i] = center + new Vector2(Mathf.Cos(anglePoint), Mathf.Sin(anglePoint)) * radius;
         }
 
-        for (int i = 0; i < nbPoints - 1; ++i)
+        for (int i = 0; i < nbPoints - 1; i++)
+        {
             DrawLine(pointsArc[i], pointsArc[i + 1], color);
+        }
     }
 
 
@@ -292,10 +294,10 @@ the same as before, except that we draw a polygon instead of lines:
         pointsArc[0] = center;
         var colors = new Color[] { color };
 
-        for (int i = 0; i < nbPoints; ++i)
+        for (int i = 0; i <= nbPoints; i++)
         {
             float anglePoint = Mathf.Deg2Rad(angleFrom + i * (angleTo - angleFrom) / nbPoints - 90);
-            pointsArc[i + 1] = center + new Vector2(Mathf.Cos(anglePoint), Mathf.Sin(anglePoint)) * radius;
+            pointsArc[i] = center + new Vector2(Mathf.Cos(anglePoint), Mathf.Sin(anglePoint)) * radius;
         }
 
         DrawPolygon(pointsArc, colors);