silence coverity warnings

(cherry picked from commit 45b727f651)

bin/tests/task_test.c

@@ -69,9 +69,13 @@ main(int argc, char *argv[]) {
 	isc_timer_t *ti1, *ti2;
 	struct isc_interval interval;
 
-	if (argc > 1)
+	if (argc > 1) {
 		workers = atoi(argv[1]);
-	else
+		if (workers < 1)
+			workers = 1;
+		if (workers > 8192)
+			workers = 8192;
+	} else
 		workers = 2;
 	printf("%d workers\n", workers);