Do not cut off an icon filename (passed to -i) at the first comma
character. The original motivation probably was to support a list of
icon names in -i separated by comma. However, this has never been
implemented and the help text for -i also only mentions "an icon".
Hence, no functionality is lost by this change. In contrast, -i now
supports commas in icon filepaths.
https://gitlab.gnome.org/GNOME/libnotify/-/issues/16