gio: `DataInputStream::read_line_async()` can return `None` slices#1803

sdroege merged 2 commits intogtk-rs:maingtk-rs/gtk-rs-core:mainfrom

sdroege:gio-data-input-stream-read-linesdroege/gtk-rs-core:gio-data-input-stream-read-lineCopy head branch name to clipboard