usp10: Check if corresponding headers are present before accessing their feature lists in _initialize_feature_cache.

Based on feedback from Henri, fixes regression from commit
63bcfa33.
Signed-off-by: Jacek Caban <jacek@codeweavers.com>
Signed-off-by: Henri Verbeet <hverbeet@codeweavers.com>
Signed-off-by: Aric Stewart <aric@codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>