skip when node size is zero

[a5-stable]

JsonPath.on({}, "[*]")
#-> lib/jsonpath/enumerable.rb:88:in `%': divided by 0 (ZeroDivisionError)

Greetings, I got an error as above and I fixed it in this pr.
this happens when node size is zero in jsonpath enumerable.

start_idx %= node.size
end_idx %= node.size

[joshbuddy]

Thanks @a5-stable