Bug: withReadableRange/limitReadableRange

[lchenut]

With this simple code:

import stew/byteutils
import faststreams

proc readAll(s: InputStream): seq[byte] =
  while s.readable:
    result.add s.read

let s = fileInput("AlphabetFile") # A => Z, 26 characters file
for _ in 0..5:
  if s.readable(4):
    s.withReadableRange(4, r):
      echo string.fromBytes(r.readAll)

I got this output:

ABCD
/home/lchenut/minnim/sf/faststreams/inputs.nim(363) lol
/home/lchenut/minnim/sf/faststreams/inputs.nim(351) limitReadableRange
/home/lchenut/.choosenim/toolchains/nim-1.6.6/lib/system/fatal.nim(53) sysFatal
Error: unhandled exception: over- or underflow [OverflowDefect]

I tried to figure out why it's failing (or even if it's an expected result) for the last two days, with no luck.