
Fixes https://github.com/flutter/flutter/issues/147189
This allows const `IconData` to fallback to the system font if `fontFamily` is not provided.
A similar non-fatal error occurs when IconData specifies a font that is not included in the manifest, so I modeled after that error message:
b4121a1867/packages/flutter_tools/lib/src/build_system/targets/icon_tree_shaker.dart (L122)