Updated lib/util.js for avoiding TypeError: Not a string or buffer

[statefull]

Avoid error TypeError: Not a string or buffer when calling api request pubkeys/register?keys=

Explanation:

In addressToPubKeyHash decoding a base58 address (bitcoin address) returns a byte array but twoSha256, concretely, sha256 requires a string or a buffer, so, to avoid errors performing sha256, the returned byte array is converted to a buffer.

[MidnightLightning]

It appears that function isn't really used in the application at all (I can't find a reference to addressToPubKeyHash other than its declaration). Are you using it in part of a child implementation that's failing? I'm wondering if the proper response is to remove it entirely if it's not used as part of the application.

[statefull]

Hi,

Yes, it is used in exit API at mods/exit/pubkeys.js line 254

// Convert Bitcoin address to pubkey hash
var pubKeyHash = Util.addressToPubKeyHash(keys[i]);