channel_folders: Add help function to check if user has sub in folder.

This commit adds a function that returns true if user is subscribed
to a channel which is in a channel folder.

web/src/channel_folders.ts

@@ -73,6 +73,18 @@ export function get_channel_folder_by_id(folder_id: number): ChannelFolder {
     return channel_folder;
 }
 
+export function user_has_folders(): boolean {
+    const subscribed_subs = stream_data.subscribed_subs();
+
+    for (const sub of subscribed_subs) {
+        if (sub.folder_id) {
+            return true;
+        }
+    }
+
+    return false;
+}
+
 export function update(event: ChannelFolderUpdateEvent): void {
     const folder_id = event.channel_folder_id;
     const channel_folder = get_channel_folder_by_id(folder_id);

web/tests/channel_folders.test.cjs

@@ -89,6 +89,9 @@ run_test("basics", () => {
         folder_id: frontend_folder.id,
     });
     stream_data.add_sub(stream_1);
+
+    assert.deepEqual(channel_folders.user_has_folders(), false);
+
     stream_data.add_sub(stream_2);
     stream_data.add_sub(stream_3);
     stream_data.add_sub(stream_4);
@@ -120,4 +123,6 @@ run_test("basics", () => {
         channel_folders.get_channels_in_folders_matching_seach_term_in_folder_name("Nonexistent"),
         [],
     );
+
+    assert.deepEqual(channel_folders.user_has_folders(), true);
 });