frontend: fallback to first channel if the selected channel cant be found

frontend/src/stores.js

@@ -49,6 +49,8 @@ class ChannelsStore extends Store {
                     const index = this.value.findIndex(e => e.id === selectedChannel.value.id);
                     if (index !== -1)
                         selectedChannel.set(this.value[index]);
+                    else // if the channel doesn't exist, just select the first one
+                        selectedChannel.set(channels[0]);
                 }
             }
             this.updated();