Bug: Inflate produces very small corner in offset

[Ayamur0]

When inflating the path in this example, it creates a very small edge in the offset.

This small error causes issues when using ZCallbacks because the edges we get in the ZCallback do not make sense, since this corner should not be there, producing Z values that don't make sense.

Something similar and more obvious happens when using JoinType.Bevel (instead of Round like in the code below). Here a weird jagged edge appears on the right:

Here is a small code sample with minimal points to reproduce this error:

public static void Main()
{
  var path = new PathsD
  {
      new PathD
        {
            new PointD(-13.027999877929688, 9.385499954223633),
            new PointD(-13.038999557495117, 9.331500053405762),
            new PointD(-13.041000366210938, 9.319499969482422),
            new PointD(-15.026000022888184, 9.319499969482422),
            new PointD(-15.024999618530273, 9.327500343322754),
        },
  };

  double scale = Math.Pow(10, 6);
  Paths64 paths64 = Clipper.ScalePaths64(path, scale);
  ClipperOffset clipperOffset = new() { };
  clipperOffset.AddPaths(paths64, JoinType.Round, EndType.Polygon);
  Paths64 solution = new();
  clipperOffset.Execute(3 * scale, solution);

  // Bug: There is a 90° small edge in the resulting offset polygon
  // Detect a roughly 90° edge in the offset polygon
  foreach (var p in solution)
  {
    for (int i = 0; i < p.Count; i++)
    {
      var prev = p[(i - 1 + p.Count) % p.Count];
      var curr = p[i];
      var next = p[(i + 1) % p.Count];

      long dx1 = curr.X - prev.X;
      long dy1 = curr.Y - prev.Y;

      long dx2 = next.X - curr.X;
      long dy2 = next.Y - curr.Y;

      double angle1 = Math.Atan2(dy1, dx1);
      double angle2 = Math.Atan2(dy2, dx2);

      double diff = Math.Abs((angle2 - angle1) * 180.0 / Math.PI);
      if (diff > 180)
        diff = 360 - diff;

      if (Math.Abs(diff - 90) < 5)
      {
        Console.WriteLine($"90° corner at ({curr.X}, {curr.Y})");
      }
    }
  }
}