clients/simple-dmabuf-egl: don't add INVALID to modifier list
While this is harmless because gbm_bo_create_with_modifiers will just fail, it's easy to misunderstand that gbm_bo_create_with_modifiers accepts MOD_INVALID. Let's just keep modifiers_count to zero instead and stop even trying to call that function with invalid input.
Stop using modifiers_count to decide whether the compositor supports a format. Instead use a separate format_supported flag.
Signed-off-by: Simon Ser contact@emersion.fr
References: mesa/mesa!7601 (comment 778845)