settings_streams: Fix error thrown when adding 'default-channels'.

The 'Select channel' dropdown in 'Add default channels' modal is
the LAST dropdown element on the modal and it does not contain
`data-stream-id` attribute.

.attr('data-stream-id') would return undefined for this element
and as a result the returned `Set` would have its last element a
`NaN` --- passing a `NaN` inside 'data' field of 'channel.post' threw
an error.

We tweaked the selector string to selectively map over the elements with
'data-stream-id' attribute.
Also we removed '.toString()' converting stream-id to a string (stream-id is a
'number' type).

web/src/settings_streams.js

@@ -28,8 +28,11 @@ function add_choice_row($widget) {
 function get_chosen_default_streams() {
     // Return the set of stream id's of streams chosen in the default stream modal.
     return new Set(
-        $("#default-stream-choices .choice-row .dropdown_widget_value")
-            .map((_i, elem) => Number($(elem).attr("data-stream-id")).toString())
+        // Note: We selectively map through the dropdown elements that contain the
+        // `data-stream-id` attribute to avoid adding an element with undefined value
+        //  into the returned `Set`.
+        $("#default-stream-choices .choice-row .dropdown_widget_value[data-stream-id]")
+            .map((_i, elem) => Number($(elem).attr("data-stream-id")))
             .get(),
     );
 }

web/src/stream_data.ts

@@ -296,12 +296,12 @@ export function delete_sub(stream_id: number): void {
     stream_info.delete(stream_id);
 }
 
-export function get_non_default_stream_names(): {name: string; unique_id: string}[] {
+export function get_non_default_stream_names(): {name: string; unique_id: number}[] {
     let subs = [...stream_info.values()];
     subs = subs.filter((sub) => !is_default_stream_id(sub.stream_id) && !sub.invite_only);
     const names = subs.map((sub) => ({
         name: sub.name,
-        unique_id: sub.stream_id.toString(),
+        unique_id: sub.stream_id,
     }));
     return names;
 }

web/tests/stream_data.test.js

@@ -491,7 +491,7 @@ test("default_stream_names", () => {
     stream_data.add_sub(general);
 
     const names = stream_data.get_non_default_stream_names();
-    assert.deepEqual(names.sort(), [{name: "public", unique_id: "102"}]);
+    assert.deepEqual(names.sort(), [{name: "public", unique_id: 102}]);
 
     const default_stream_ids = stream_data.get_default_stream_ids();
     assert.deepEqual(default_stream_ids.sort(), [announce.stream_id, general.stream_id]);