sd fails on empty files -- v0.74

[ms-jpq]

Hi there,

Thank you for making sd, it honestly makes my life so much easier :D

I noticed that there was an closed issue #74 with a comment saying that this bug is fixed for v0.74, but it still seems to happen on MacOS.

❯ touch file
❯ sd -p '5' '' file
Error: memory map must have a non-zero length
❯ sd --version
sd 0.7.4

Darwin IIIII.lan 19.4.0 Darwin Kernel Version 19.4.0: