Shifting bits to 0-length BitVectors fails

[kleinreact]

Shifting a bit into a 0-length BitVector with (+>>.) or (.<<+) currently fails with an out of range exception.

We should either define the operations to keep empty bit vectors unchanged or exclude them from the interface via adding some 1 <= n constraints.

The former would be the way to go in order to stay consistent with (+>>) and (<<+):

clashi> high +>> (Nil :: Vec 0 Bit)
Nil
clashi> (Nil :: Vec 0 Bit) <<+ low
Nil

[christiaanb]

We've released v1.8.2, which includes a fix for this issue.