Broken tabs at target NS if key == NS_name

If the tab key in $wgNamespaceRelations was equal to the extra
namespace, it would lead to assigning wrong keys into
pre-$navigation array and thus rewriting some tabs.

Change-Id: I9fe57285559b9b256c47d95dcc43ec24baec05d9
Merge "Broken tabs at target NS if key == NS_name"