Fixes #39: Todo crashes when space pressed with no selection

todo/list.go

@@ -24,6 +24,10 @@ func (list *List) Delete() {
 }
 
 func (list *List) Demote() {
+	if list.isUnselectable() {
+		return
+	}
+
 	j := list.selected + 1
 	if j >= len(list.Items) {
 		j = 0
@@ -48,6 +52,10 @@ func (list *List) Prev() {
 }
 
 func (list *List) Promote() {
+	if list.isUnselectable() {
+		return
+	}
+
 	j := list.selected - 1
 	if j < 0 {
 		j = len(list.Items) - 1
@@ -58,7 +66,7 @@ func (list *List) Promote() {
 }
 
 func (list *List) Selected() *Item {
-	if list.selected < 0 || list.selected >= len(list.Items) {
+	if list.isUnselectable() {
 		return nil
 	}
 
@@ -67,6 +75,10 @@ func (list *List) Selected() *Item {
 
 // Toggle switches the checked state of the selected item
 func (list *List) Toggle() {
+	if list.isUnselectable() {
+		return
+	}
+
 	list.Items[list.selected].Toggle()
 }
 
@@ -97,3 +109,13 @@ func (list *List) Less(i, j int) bool {
 func (list *List) Swap(i, j int) {
 	list.Items[i], list.Items[j] = list.Items[j], list.Items[i]
 }
+
+/* -------------------- Unexported Functions -------------------- */
+
+func (list *List) isSelectable() bool {
+	return list.selected >= 0 && list.selected < len(list.Items)
+}
+
+func (list *List) isUnselectable() bool {
+	return !list.isSelectable()
+}