Fix test-dump-cache-tree in one-tree disappeared case.
Fix test-dump-cache-tree in one-tree disappeared case.

When reconstructing an invalidated subtree for reference purposes by
test-dump-cache-tree, we did not handle the case where we shouldn't
have a cached and invalidated subtree in the result, leading to an
unneeded die().

Signed-off-by: Junio C Hamano <dc50d1021234060e53ec42a77d526afa2fe07479@cox.net>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git