Clean up a warning when iterating large search results.

If you do a search that returns more results than your
$TicketsItemMapSize then Tickets->ItemMap sets the last link to 'undef'
because it doesn't know the last result in the set (it only knows the
subset).  Unfortunately, this caused warnings in two places that were
only checking for 'next' and assuming 'last' would be defined.
Merge branch '4.0/silence-last-search-warning' into 4.0-trunk

Conflicts:
	share/html/Elements/Tabs