Can't open empty files
At least the mmap and malloc backends aren't able to open a file that has length equal to zero. It seems like they can't tell the difference between a zero length file and an I/O error while trying to open the file. See, for example, src/hex-buffer-mmap.c:684
To reproduce: touch
a new file, then try to open that file in GHex.
Expected behavior: It seems reasonable to be able to open an empty file, add some bytes, and then save it.