Subrecords cannot overlap records

Subrecords that go out of bounds of the record due to an improperly set size effectively cause UB in OpenMW but are handled "correctly" in Morrowind and TESCS, as the full record size is still respected by its ESM reader when it goes to the beginning of the next record. However, both Morrowind and OpenMW use the full subrecord size to determine its contents.

This must be fixed to get version 1.0 of this mod to work. The mod contains two books and the text of the first book overlaps the second book's definition.