When the "${native_assets_path}"*.framework glob doesn't resolve anything, the bash will run the loop once with the original unglobbed value: /path/to/native/assets/*.framework. Skip this case to prevent the build from failing when there are no frameworks to sign.

To reproduce this build failure:

1. Enable native assets in the Flutter tool: flutter config --enable-native-assets
2. Create a Flutter project with the default template: flutter create test_native_assets
3. Add a build hook that does nothing (hook/build.dart).
4. Try to build/run the app: flutter run --debug -d macos