Comment 0 for bug 1694697

If the last alternative(s) of an Or group is ignored, because it does
not match an architecture list, we would end up keeping the or flag,
effectively making the next AND an OR.

For example, when parsing (on amd64):

    debhelper (>= 9), libnacl-dev [amd64] | libnacl-dev [i386]
 => debhelper (>= 9), libnacl-dev |

Which can cause python-apt to crash.

Even worse:

     debhelper (>= 9), libnacl-dev [amd64] | libnacl-dev [i386], foobar
  => debhelper (>= 9), libnacl-dev [amd64] | foobar

By setting the previous alternatives Or flag to the current Or flag
if the current alternative is ignored, we solve the issue.