fix: a bunch of stuff related to multitasking

src/multitasking/scheduler.c

@@ -10,7 +10,7 @@ void scheduler(void)
 	if (!current_task)
 		return;
 	struct task *it = current_task->next;
-	while (it->status != RUN)
+	while (it && it->status != RUN)
 		it = it->next;
 	switch_to_task(it);
 }