Fixes ReadOnlyNativePtrArray.IndexOf returning invalid index.

PkmnLibSharp/Utilities/ReadOnlyNativePtrArray.cs

@@ -62,10 +62,10 @@ namespace PkmnLibSharp.Utilities
         {
             for (var i = 0; i < Count; i++)
             {
-                var p = _ptr + (i * IntPtr.Size);
-                if (item == null)
+                var p = GetPtr(i);
+                if (item == null && p == IntPtr.Zero)
                     return i;
-                if (p == item.Ptr)
+                if (p == item?.Ptr)
                     return i;
             }
             return -1;