Fix/KFS-1682 completion on down (#42)

* fix: small bug with completion on down and history

* fix: lint

_example/multiline-echo/main.go

@@ -21,6 +21,7 @@ func main() {
 	in := prompt.Input(">>> ", completer,
 		prompt.OptionTitle("sql-prompt"),
 		prompt.OptionHistory([]string{"SELECT * FROM users;"}),
+		prompt.OptionCompletionOnDown(),
 		prompt.OptionPrefixTextColor(prompt.Yellow),
 		prompt.OptionPreviewSuggestionTextColor(prompt.Blue),
 		prompt.OptionSelectedSuggestionBGColor(prompt.LightGray),

history.go

@@ -35,6 +35,10 @@ func (h *History) Older(buf *Buffer) (new *Buffer, changed bool) {
 	return new, true
 }
 
+func (h *History) HasNewer() bool {
+	return h.selected < len(h.tmp)-1
+}
+
 // Newer saves a buffer of current line and get a buffer of next line by up-arrow.
 // The changes of line buffers are stored until new history is created.
 func (h *History) Newer(buf *Buffer) (new *Buffer, changed bool) {

prompt.go

@@ -329,6 +329,7 @@ func (p *Prompt) feed(b []byte) (shouldExit bool, exec *Exec) {
 				// move the cursor up by one line
 				p.buf.CursorDown(1)
 			} else if newBuf, changed := p.history.Newer(p.buf); changed {
+
 				p.prevText = p.buf.Text()
 				p.buf = newBuf
 			}
@@ -354,9 +355,10 @@ func (p *Prompt) feed(b []byte) (shouldExit bool, exec *Exec) {
 }
 
 func (p *Prompt) handleCompletionKeyBinding(key Key, completing bool) {
+
 	switch key {
 	case Down:
-		if completing || p.completionOnDown {
+		if completing || (p.completionOnDown && !p.history.HasNewer()) {
 			p.completion.Next()
 		}
 	case Tab, ControlI: