bug#26576: -v when used with -C

[積丹尼 Dan Jacobson]

You know if this only gets five lines,
grep -C 2    ZZZ 00001.vcf|wc - 00001.vcf
      5       5     197 -
   1686    1731   83630 00001.vcf
then this
grep -C 2 -v ZZZ 00001.vcf|wc - 00001.vcf
   1686    1731   83630 -
   1686    1731   83630 00001.vcf
should get all EXCEPT five lines.