Fix: invalid handling of empty channels list.

When channels list is empty, up/down and default selection used
invalid index 0.

src/app.rs

@@ -149,7 +149,7 @@ impl App {
                 data
             }
         };
-        if data.channels.state.selected().is_none() {
+        if data.channels.state.selected().is_none() && !data.channels.items.is_empty() {
             data.channels.state.select(Some(0));
             data.save(&config.data_path)?;
         }

src/ui.rs

@@ -104,7 +104,8 @@ fn draw_messages<B: Backend>(f: &mut Frame<B>, app: &App, area: Rect) {
         .channels
         .state
         .selected()
-        .map(|idx| &app.data.channels.items[idx].messages[..])
+        .and_then(|idx| app.data.channels.items.get(idx))
+        .map(|channel| &channel.messages[..])
         .unwrap_or(&[]);
 
     let max_username_width = messages

src/util.rs

@@ -25,7 +25,13 @@ impl<T> StatefulList<T> {
                     i + 1
                 }
             }
-            None => 0,
+            None => {
+                if !self.items.is_empty() {
+                    0
+                } else {
+                    return; // nothing to select
+                }
+            }
         };
         self.state.select(Some(i));
     }
@@ -39,7 +45,13 @@ impl<T> StatefulList<T> {
                     i - 1
                 }
             }
-            None => 0,
+            None => {
+                if !self.items.is_empty() {
+                    0
+                } else {
+                    return; // nothing to select
+                }
+            }
         };
         self.state.select(Some(i));
     }