Bug 891984: Properly render contacts in favorites.

Previously if a contact was a favorite, then we would only render it once
in either its main letter group or the favorites group.  This patch correctly
tracks the group so that we reference the contact properly in order to
render it for both groups.
Merge pull request #10902 from wanderview/contacts-favorites

Bug 891984: Properly render contacts in favorites.  r=crdlc