Clip truncated sectors at true end of data
Clip truncated sectors at true end of data

8K sectors stored in single revolution images hold just one
truncated copy of the sector data. We now clip the data where it
ends, rather than attempting to continue to the next header field.

This fixes the junk at the end of Les Barbares [A].scp tracks.

simonowen/samdisk,simonowen/samdisk,simonowen/samdisk