GitLab

gbm: fail early when modifier list only contains INVALID

The current check only accomodates for a list with a single INVALID
item. However the driver won't be able to pick any modifier if the
list only contains INVALID. This includes the following cases:

- The modifier list is empty (count == 0)
- The modifier list contains more than a single item, but all items
  are INVALID

In these cases, also fail early.

Signed-off-by: Simon Ser <contact@emersion.fr>
References: mesa/mesa!7601 (comment 778845)