Internal Bug

I use SimdJsonSharp.Managed.

```
Exception has occurred: CLR/System.InvalidOperationException
An unhandled exception of type 'System.InvalidOperationException' occurred in SimdJsonSharp.Managed.dll: 'Internal bug'
at SimdJsonSharp.stage1_find_marks.find_structural_bits(Byte* buf, UInt64 len, ParsedJson pj)
at SimdJsonSharp.SimdJson.JsonParse(Byte* jsonData, UInt64 length, ParsedJson pj, Boolean reallocIfNeeded)
at SimdJsonSharp.SimdJson.ParseJson(Byte* jsonData, Int32 length, Boolean reallocIfNeeded)
at JsonTest.Program.Main(String[] args) in c:\Users\hez20\Desktop\JsonTest\Program.cs:line 14
```

test code:
```csharp
using System;
using System.Text;
using SimdJsonSharp;

namespace JsonTest
{
class Program
{
static unsafe void Main(string[] args)
{
var p = Encoding.UTF8.GetBytes("{\"test\": 1}");
fixed (byte* ptr = p)
{
var json = SimdJson.ParseJson(ptr, p.Length);
}
return;
}
}
}
```