not a sequence panic involving empty sequences

[RyanGlScott]

The following program causes Cryptol to panic when evaluated:

// Main.cry

f : [0] -> [inf][0]
f = split

main : [0]
main = (f []) @ 0

$ ~/Software/cryptol-3.2.0/bin/cryptol Main.cry -c 'main'
Loading module Cryptol
Loading module Main
cryptol: You have encountered a bug in Cryptol's implementation.
*** Please create an issue at https://github.com/GaloisInc/cryptol/issues

%< --------------------------------------------------- 
  Revision:  1bcb75c5be92034b7b29155ab1f5d72780838605
  Branch:    release-3.2.0 (uncommited files present)
  Location:  [Eval] fromSeq
  Message:   not a sequence
             splitV
             word:0
CallStack (from HasCallStack):
  panic, called at src/Cryptol/Utils/Panic.hs:21:9 in cryptol-3.2.0-inplace:Cryptol.Utils.Panic
  panic, called at src/Cryptol/Backend/Monad.hs:410:17 in cryptol-3.2.0-inplace:Cryptol.Backend.Monad
  evalPanic, called at src/Cryptol/Eval/Value.hs:413:18 in cryptol-3.2.0-inplace:Cryptol.Eval.Value
%< ---------------------------------------------------