GtkPrintJob set_source_fd/file leaks existing IO channel
When using both gtk_print_job_set_source_fd()
and gtk_print_job_set_source_file()
on the same GtkPrintJob
(as xdg-desktop-portal-gnome
does at here and here), the existing priv->spool_io
channel is leaked since neither function clears it before assigning a new object.
gtk-3-24 (also present on master)