(a) INFRINGER'S CIVIL ACTION.- (1) POST-GRANT REVIEW BARRED BY CIVIL ACTION.-A post-grant review may not be instituted under this chapter if, before the date on which the petition for such a review is filed, the petitioner or real party in interest filed a civil action challenging the validity of a claim of the patent. (2) STAY OF CIVIL ACTION.-If the petitioner or real party in interest files a civil action challenging the validity of a claim of the patent on or after the date on which the petitioner