Fix remaining _volumeHandle references to _handle in ReadMftRecordSize and Dispose

FastSeekWpf/Core/MftReader.cs

@@ -240,11 +240,11 @@ public class MftReader : IDisposable
     // Read MFT record size from NTFS boot sector — matches Rust read_mft_record_size()
     private int? ReadMftRecordSize()
     {
-        Win32Api.SetFilePointerEx(_volumeHandle, 0, out _, 0);
+        Win32Api.SetFilePointerEx(_handle, 0, out _, 0);
 
         byte[] boot = new byte[512];
         uint br = 0;
-        bool ok = Win32Api.ReadFile(_volumeHandle, boot, 512, out br, IntPtr.Zero);
+        bool ok = Win32Api.ReadFile(_handle, boot, 512, out br, IntPtr.Zero);
         if (!ok || br < 512)
             return null;
 
@@ -401,7 +401,7 @@ public class MftReader : IDisposable
     {
         if (!_disposed)
         {
-            Win32Api.CloseHandle(_volumeHandle);
+            Win32Api.CloseHandle(_handle);
             _disposed = true;
         }
         GC.SuppressFinalize(this);