sparse-read: ignore trailing empty revs in each read chunk An empty entry in the revlog may happen for two reasons: - when the file is empty, and the revlog stores a snapshot; - when there is a merge and both parents were identical. `hg debugindex -m | awk '$3=="0"{print}' | wc -l` gives 1917 of such entries in my clone of pypy, and 113 on my clone of mercurial. These empty revision may be located at the end of a sparse chain, and in some special cases may lead to read relatively large amounts of data for nothing.