fix(ui): set project to empty string if undefined (#18732)

There are some situations where the project will be `undefined`. When
that happens, attempting to delete a repo won't be possible, since
the backend will be looking for a project with the literal name
`undefined`. To fix this, set an empty string for `undefined|null`
values.

Signed-off-by: Blake Pettersson <blake.pettersson@gmail.com>

ui/src/app/settings/components/repos-list/repos-list.tsx

@@ -857,7 +857,7 @@ export class ReposList extends React.Component<
         const confirmed = await this.appContext.apis.popup.confirm('Disconnect repository', `Are you sure you want to disconnect '${repo}'?`);
         if (confirmed) {
             try {
-                await services.repos.delete(repo, project);
+                await services.repos.delete(repo, project || '');
                 this.repoLoader.reload();
             } catch (e) {
                 this.appContext.apis.notifications.show({