Fix activity leak in Dialer

Make sure to close the contact lookup thread when ListsFragment is
destroyed, just like in CallLogFragment.

The thread was holding a reference to the outer adapter because it was
a non-static inner class, which was causing the adapter and activity to
leak.

Bug: 17472228
Change-Id: Ic2d6fbded0c8c40cf99d779fe24a535d75bc802a