rawEncode silently accepts invalid hex strings

[lionello]

Actual

$ node
> require('ethereumjs-abi').rawEncode(["uint256"], "g")
<Buffer 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 10>

The string "g" gets interpreted as "f"+1.

Expected

Calling rawEncode with invalid number or hex string should throw.

[sc0Vu]

Maybe check value in this function: encodeSingle ?