wifi: iwlwifi: pcie: avoid a NULL pointer dereference

It possible that while the rx rb is being handled, the transport has
been stopped and re-started. In this case the tx queue pointer is not
yet initialized, which will lead to a NULL pointer dereference.
Fix it.
Signed-off-by: Avraham Stern <avraham.stern@intel.com>
Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://msgid.link/20231207044813.cd0898cafd89.I0b84daae753ba9612092bf383f5c6f761446e964@changeidSigned-off-by: Johannes Berg <johannes.berg@intel.com>

drivers/net/wireless/intel/iwlwifi/pcie/rx.c

@@ -1385,7 +1385,7 @@ static void iwl_pcie_rx_handle_rb(struct iwl_trans *trans,
 		 * if it is true then one of the handlers took the page.
 		 */
 
-		if (reclaim) {
+		if (reclaim && txq) {
 			u16 sequence = le16_to_cpu(pkt->hdr.sequence);
 			int index = SEQ_TO_INDEX(sequence);
 			int cmd_index = iwl_txq_get_cmd_index(txq, index);