`sort-lines' on the empty region

[Simen Heggestøyl]

The current behavior of `sort-lines' on the empty region is to do
nothing. I often find that I want to sort whole buffers at the time,
and I expect `sort-lines' to do just that, before remembering I have
to mark the whole buffer first.

Wouldn't it be convenient to change the behavior of `sort-lines' so
that it sorts the whole buffer if no region is marked? Or is this
inconsistent with how other region-operating functions works?