Parse error might occur one line earlier

Because of the change in implementation of VCF, errors might be reported when reading the previous line.

The log message (disabled unless the compilation variable DEBUG is set) will indicate the correct line.

The ad hoc solution to fix it might be to believe the result of bcf_sr_next_line() (ignore errnum, as we did just before) and check that errnum is not set before attempting to read.

But what will happen if we call goto() after errnum has been set? Will it be resetted?