Handle bad indices in MemoryListModel
Handle bad indices in MemoryListModel

Makes sure that MemoryListModel returns correct values when bad indices are
given. This makes it compatible with how Banshee's MemoryListModel works.

Without this, grid view crashes.

https://bugzilla.gnome.org/show_bug.cgi?id=616710

rubenv/tripod,rubenv/tripod