[purge.c] fixed infinite loop when initial excess is negative
[purge.c] fixed infinite loop when initial excess is negative

mancoast/cado-nfs,mancoast/cado-nfs,mancoast/cado-nfs,mancoast/cado-nfs,mancoast/cado-nfs,mancoast/cado-nfs,mancoast/cado-nfs