Fix error propagation in iterator

index.js

@@ -830,7 +830,7 @@ Blockchain.prototype._iterator = function (name, func, cb) {
     async.whilst(
       () => blockNumber,
       run,
-      () => self._saveHeads(cb)
+      (err) => err ? cb(err) : self._saveHeads(cb)
     )
   })
 

test/index.js

@@ -11,7 +11,7 @@ const testData = require('./testdata.json')
 const BN = require('bn.js')
 
 test('blockchain test', function (t) {
-  t.plan(59)
+  t.plan(61)
   var blockchain = new Blockchain()
   var genesisBlock
   var blocks = []
@@ -220,6 +220,15 @@ test('blockchain test', function (t) {
         done()
       })
     },
+    function iterateError (done) {
+      blockchain.iterator('error', function (block, reorg, cb) {
+        cb(new Error('iterator func error'))
+      }, function (err) {
+        t.ok(err, 'should catch iterator func error')
+        t.equal(err.message, 'iterator func error', 'should return correct error')
+        done()
+      })
+    },
     function iterateEmpty (done) {
       var blockchain = new Blockchain()
       blockchain.validate = false