goption: Option parsing recognizes group options with three dashes
Group options specified with three dashes (i.e. ---foo 42) on the command line are recognized by goption, but main entry options are not.
The issue stems from the '--<group>-<option>' handling in g_option_context_parse.
Not sure if this would be considered expected behavior, but the "fix" is trivial (I'll open a PR shortly).