[SCSI] libiscsi: fix possbile null ptr session command cleanup

If the iscsi eh fires when the current task is a nop, then
the task->sc pointer is null. fail_all_commands could
then try to do task->sc->device and oops. We actually do
not need to access the curr task in this path, because
if it is a cmd task the fail_command call will handle
this and if it is mgmt task then the flush of the mgmt
queues will handle that.

Signed-off-by: Mike Christie <michaelc@cs.wisc.edu>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>

drivers/scsi/libiscsi.c

@@ -1603,8 +1603,11 @@ static void fail_all_commands(struct iscsi_conn *conn, unsigned lun,
 {
 	struct iscsi_task *task, *tmp;
 
-	if (conn->task && (conn->task->sc->device->lun == lun || lun == -1))
-		conn->task = NULL;
+	if (conn->task) {
+		if (lun == -1 ||
+		    (conn->task->sc && conn->task->sc->device->lun == lun))
+			conn->task = NULL;
+	}
 
 	/* flush pending */
 	list_for_each_entry_safe(task, tmp, &conn->xmitqueue, running) {