glib/spawn: check user source_fds doesn't contain private fds
If the user provided source_fds set contains internal fds, this is a programmer mistake. We can avoid further damage by preventing this situation.
Originally from !2458 (merged)
If the user provided source_fds set contains internal fds, this is a programmer mistake. We can avoid further damage by preventing this situation.
Originally from !2458 (merged)