Changes

Process all "have"s even when MissingObjectException is encountered

Because objects described by the client using "have" lines do not need
to be reachable by any ref on the server, it is possible for them to
point to missing objects in the reachability graph.  When such an
object is encountered, I1097a2defa4a9dcf502ca8baca5d32880378818f (Only
throw MissingObjectException when necessary, 2017-03-29) aborts the
"have" walk early to salvage the fetch.  The downside of that change
is that remaining "have"s are ignored unless they pointed directly to
an object with a bitmap.  In the worst case this can increase the
bandwidth cost of a fetch to the cost of a clone because most "have"s
are ignored.

Avoid this cost by bypassing the failed "have" completely and moving
on to the remaining "have"s.

Change-Id: Iac236b6d05f735078c9935abfa6e58d1eb47f388