scheduler: fix issue with threads being lost

kernel-src/lib/semaphore.c

@@ -114,6 +114,7 @@ void semaphore_signal(semaphore_t *sem) {
 			// wake SOMEONE up. this will *try* to wake up a thread
 			// it could wake up none though, as a thread could have been interrupted by a signal
 			thread = get(sem);
+			// TODO this is broken
 			// XXX the current method doesn't respect thread priorities
 			if (thread) {
 				sched_wakeup(thread, 0);

kernel-src/sys/scheduler.c

@@ -546,7 +546,11 @@ static void yield(context_t *context, void *) {
 
 	if (sleeping && (thread->shouldexit || gotsignal) && (thread->flags & SCHED_THREAD_FLAGS_INTERRUPTIBLE)) {
 		sleeping = false;
+
+		if (next)
+			runqueueinsert(next);
 		next = NULL;
+
 		thread->flags &= ~(SCHED_THREAD_FLAGS_SLEEP | SCHED_THREAD_FLAGS_INTERRUPTIBLE);
 		thread->wakeupreason = SCHED_WAKEUP_REASON_INTERRUPTED;
 		spinlock_release(&thread->sleeplock);