Merge branch 'ds/sparse-index-ita-crash' into jch

A crash in the 'sparse-index' collapse code when encountering an
invalidated cache-tree node (due to an intent-to-add path) has been
fixed by avoiding collapsing such subtrees.

* ds/sparse-index-ita-crash:
  sparse-index: avoid crash on intent-to-add entry outside the cone

diff --cc t/t1092-sparse-checkout-compatibility.sh
Simple merge

diff --cc t/t3705-add-sparse-checkout.sh
Simple merge