Merge branch 'backport/jk/range-diff-fixes'

"git range-diff" code clean-up. Needed to pacify modern GCC versions.

* jk/range-diff-fixes:
  range-diff: use ssize_t for parsed "len" in read_patches()
  range-diff: handle unterminated lines in read_patches()
  range-diff: drop useless "offset" variable from read_patches()