Backport !1794 “gio-tool-info: Prevent criticals if mount options are not available” to glib-2-66
NULL is valid return value for the g_unix_mount_get_options function because mount options are currently provided only by libmount implementation. However, the gio tool passes the returned value to the g_strescape function without checking, which produces the following critical warning: GLib-CRITICAL **: 13:47:15.294: g_strescape: assertion 'source != NULL' failed
Let's add the missing check to prevent the critical warnings.
Trivial backport of !1794 (merged) to