fix virtual SD file position count

[zxy16305]

The resume process begins at self.current_file.seek(self.file_position), where self.file_position represents a byte-length offset. However, file_position is incremented by len(line), which corresponds to the string length. If there are any UTF-8 characters preceding the 'PAUSE' command, the resumed file position must be set before the occurrence of 'PAUSE'.

To address this issue, replacing the string length with the byte length is sufficient.

[KevinOConnor]

Thanks. Seems fine to me. Commits need to have a signed-off-by line for me to commit directly though - see: https://www.klipper3d.org/CONTRIBUTING.html

-Kevin

[zxy16305]

Thank you! I'll close this pull request and open another one at https://github.com/Klipper3d/klipper/pull/6472