iwlwifi: queue: bail out on invalid freeing

iwlwifi: queue: bail out on invalid freeing

[ Upstream commit 0bed6a2a14afaae240cc431e49c260568488b51c ]

If we find an entry without an SKB, we currently continue, but
that will just result in an infinite loop since we won't increment
the read pointer, and will try the same thing over and over again.
Fix this.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/iwlwifi.20210122144849.abe2dedcc3ac.Ia6b03f9eeb617fd819e56dd5376f4bb8edc7b98a@changeid
Signed-off-by: Sasha Levin <sashal@kernel.org>