ncdumpzone: Work around encoding errors

Namecoin Core 0.18.0+ now reports an empty Name with a non-empty NameError
when an encoding error was encountered.  This was causing an infinite loop
in ncdumpzone.

Fixes https://github.com/namecoin/ncdns/issues/105

ncdumpzone/ncdumpzone.go

@@ -18,7 +18,7 @@ import (
 
 var log, Log = xlog.New("ncdumpzone")
 
-const perCall = 1000
+const defaultPerCall uint32 = 1000
 
 func dumpRR(rr dns.RR, dest io.Writer, format string) error {
 	switch format {
@@ -91,6 +91,7 @@ func Dump(conn *namecoin.Client, dest io.Writer, format string) error {
 
 	currentName := "d/"
 	continuing := 0
+	perCall := defaultPerCall
 
 	for {
 		results, err := conn.NameScan(currentName, perCall)
@@ -110,6 +111,33 @@ func Dump(conn *namecoin.Client, dest io.Writer, format string) error {
 			continuing = 1
 		}
 
+		// Temporary hack to fix
+		// https://github.com/namecoin/ncdns/issues/105
+		// TODO: Replace this hack with hex encoding after Namecoin
+		// Core 0.18.0+ is ubiquitous.
+		lenResults := len(results)
+		for results[len(results)-1].NameError != "" {
+			results = results[:len(results)-1]
+
+			if len(results) == 0 {
+				break
+			}
+		}
+		// Edge case: if all of the results had a NameError,
+		// then try to get more results at once.
+		if len(results) == 0 {
+			// All of the results had a nameError but we're
+			// at the end of the results, so not a problem.
+			if lenResults < int(perCall)-1 {
+				log.Info("out of results, stopping")
+				break
+			}
+
+			log.Warnf("All %d results (start point %s) had a NameError", lenResults, currentName)
+			perCall *= 2
+			continue
+		}
+
 		for i := range results {
 			r := &results[i]