media-export: Remove container-search hack

https://bugzilla.gnome.org/show_bug.cgi?id=706059
media-export: Fix fall-back search recursion

https://bugzilla.gnome.org/show_bug.cgi?id=706058
media-export: Check contains argument

Prevent a critical when running "contains" search on nullable columns.

https://bugzilla.gnome.org/show_bug.cgi?id=706182