🐛 Fix Position getter of uninitiliazed LazyFileStream returning 0

[pleonex]

The getter of Position of a LazyFileStream (type used to open files for Nodes by default) was already returning always 0. There was already logic in place to keep the initial position set, and used when opening the file later, but it was not returned.

Quality check list

• Related code has been tested automatically or manually
• Related documentation is updated
• I acknowledge I have read and filled this checklist and accept the
  developer certificate of origin

Acceptance criteria

Accessing Position of a lazy FileStream should return the previous assigned value without opening the Stream.

Follow-up work

N/A

Example

using var stream = new LazyFileStream(filePath, FileOpenMode.ReadWrite);
Assert.That(stream.Position, Is.EqualTo(0));

stream.Position = 0x42;
Assert.That(stream.BaseStream, Is.Null);
Assert.That(stream.Position, Is.EqualTo(0x42));