Fix reading sector tag

[FakeShemp]

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• New filesystem, test images in [url]
• New media image, test images in [url]
• New partition scheme, test images in [url]
• Breaking change (fix or feature that would cause existing functionality to change)
• I have read the CONTRIBUTING document.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

Please check this carefully, but I think this bugfix is correct.

Previous code read at wrong offset when reading a sector tag from aaruf from a buffer storing multiple tags in sequence, like the CPR_MAI on DVDs and CD subchannels.

As far as I know nothing was actually affected since subchannels on CDs were always read in ReadSectorLong and no other format handled the CPR_MAI. CD subchannels could be affected though.

[claunia]

Subchannels are not affected because sector_offset is always 0 with them.