base58check: buffers only, remove explicit 0

Undefined is treated as zero if it ever gets to this point anyway, so no
value is added by having this default param here.

A test fixture to verify this behaviour is added.

src/base58check.js

@@ -4,13 +4,8 @@ var base58 = require('./base58')
 var crypto = require('./crypto')
 
 // Encode a buffer as a base58-check-encoded string
-function encode(buffer, version) {
-  version = version || 0
-
-  // FIXME: `new Buffer(buffer)` is unnecessary if input is a Buffer
+function encode(payload, version) {
   var version = new Buffer([version])
-  var payload = new Buffer(buffer)
-
   var message = Buffer.concat([version, payload])
   var checksum = crypto.hash256(message).slice(0, 4)
 

test/base58check.js

@@ -11,7 +11,7 @@ describe('base58check', function() {
       it('can decode ' + f.string, function() {
         var actual = base58check.decode(f.string)
         var expected = {
-          version: f.decode.version,
+          version: f.decode.version || 0,
           payload: h2b(f.decode.payload),
           checksum: h2b(f.decode.checksum)
         }
@@ -40,4 +40,3 @@ describe('base58check', function() {
     })
   })
 })
-

test/fixtures/base58check.json

@@ -1,5 +1,12 @@
 {
   "valid": [
+    {
+      "string": "1AGNa15ZQXAZUgFiqJ2i7Z2DPU2J6hW62i",
+      "decode": {
+        "payload": "65a16059864a2fdbc7c99a4723a8395bc6f188eb",
+        "checksum": "c046b2ff"
+      }
+    },
     {
       "string": "1AGNa15ZQXAZUgFiqJ2i7Z2DPU2J6hW62i",
       "decode": {