Fix Err fallout for graph/gaedatastore iterator

graph/gaedatastore/iterator.go

@@ -41,6 +41,7 @@ type Iterator struct {
 	offset int
 	last   string
 	result graph.Value
+	err    error
 }
 
 var (
@@ -267,7 +268,8 @@ func (it *Iterator) Next() bool {
 		}
 		if err != nil {
 			glog.Errorf("Error fetching next entry %v", err)
-			break
+			it.err = err
+			return false
 		}
 		if !skip {
 			it.buffer = append(it.buffer, k.StringID())
@@ -288,6 +290,10 @@ func (it *Iterator) Next() bool {
 	return true
 }
 
+func (it *Iterator) Err() error {
+	return it.err
+}
+
 func (it *Iterator) Size() (int64, bool) {
 	return it.size, true
 }