This introduces no functional changes, but should help guide static
analysis. Currently, scan-build thinks that match could be used after
being freed, because it assumes that _xdg_mime_magic_parse_error()
could return any XdgMimeMagicState.
See the trace here: https://gnome.pages.gitlab.gnome.org/-/glib/-/jobs/1993739/artifacts/_scan_build/meson-logs/scanbuild/2022-05-10-050755-3977-1/report-6f5f44.html#EndPath
Signed-off-by: Philip Withnall pwithnall@endlessos.org