kernel/sem: Properly handle create_sem being called with a negative count.

It doesn't make much sense to do this, and the Be Book specifies that
doing so will return an error. A user on the mailing list tested
against BeOS and confirmed that it does reject this, so we should too.

src/system/kernel/sem.cpp

@@ -468,6 +468,8 @@ haiku_sem_init(kernel_args *args)
 sem_id
 create_sem_etc(int32 count, const char* name, team_id owner)
 {
+	if (count < 0)
+		return B_BAD_VALUE;
 	if (!sSemsActive || sUsedSems == sMaxSems)
 		return B_NO_MORE_SEMS;