Called if reading the term that starts at Pos raised Error. If the
syntax error is at the end of the file we assume the last write only
partially made it to disk, e.g., because the disk was full or the
process was killed. In that case we print a warning and truncate
the file to Pos, i.e., just after the last valid term. Anything
else is re-raised.
Note that we do not repair a file from which not a single term could
be read (Pos is 0). Such a file is most likely not a persistent
database at all and we do not want to destroy it.
