Handle the case that init has no children

Fixes #183

os/src/init/main.cc

@@ -157,6 +157,7 @@ int main(int, char **)
 	catch (...) { }
 
 	/* create children */
+	try {
 		Genode::Xml_node start_node = Genode::config()->xml_node().sub_node("start");
 		for (;; start_node = start_node.next("start")) {
 
@@ -167,6 +168,10 @@ int main(int, char **)
 
 			if (start_node.is_last("start")) break;
 		}
+	}
+	catch (Genode::Xml_node::Nonexistent_sub_node) {
+		PERR("No children to start");
+	}
 
 	/* start children */
 	children.start();