'nfs' variable was set to -1 or -2 on agent failure. Cleanup then tried
to free 'nfs' elements of the array which resulted into a crash.

Make 'nfs' size_t and assign it only on successful agent call.

https://bugzilla.redhat.com/show_bug.cgi?id=1812965

Broken by commit 599ae372Signed-off-by: NPeter Krempa <pkrempa@redhat.com>
Reviewed-by: NJán Tomko <jtomko@redhat.com>