appDisplay: Fix dead error handling

gjs includes an override to turn GSettings' asserts into exceptions,
but we'll have to catch that instead of checking for a null return
value.

Spotted by coverity in CID 351268.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1950>

js/ui/appDisplay.js

@@ -1831,11 +1831,13 @@ class AppDisplay extends BaseAppView {
 
         // Create the new folder
         let newFolderPath = this._folderSettings.path.concat('folders/', newFolderId, '/');
-        let newFolderSettings = new Gio.Settings({
+        let newFolderSettings;
+        try {
+            newFolderSettings = new Gio.Settings({
                 schema_id: 'org.gnome.desktop.app-folders.folder',
                 path: newFolderPath,
             });
-        if (!newFolderSettings) {
+        } catch (e) {
             log('Error creating new folder');
             return false;
         }