take 2: fix assert_nexus for partially delivered / unpended subtrees

The previous commit went in the right direction, but was not correct.

For CHK_ORDER, we must only ever look at type != T_NEXUS and check any
T_NEXUS by the criteria originally passed.

CHK_ORDER could be stricter still, after a subtree is completed, we
could communicate up the stricter CHK_PEND, but I do not want to
complicate things further for an assertion.

src/node_assert.h

@@ -51,18 +51,28 @@ enum check_state {
 static inline void assert_node(struct node *node, enum check_state check);
 
 static inline void
-assert_nexus(struct node *node, enum check_state check)
+assert_nexus(struct node *node, enum check_state nexcheck)
 {
 	struct node *child;
+	enum check_state check;
 
 	CHECK_OBJ_NOTNULL(node, NODE_MAGIC);
 	assert(node->type == T_NEXUS);
 
+	check = nexcheck;
 	VSTAILQ_FOREACH(child, &node->nexus.children, sibling) {
+		if (child->type == T_NEXUS) {
+			/*
+			 * actually, we would need to communicate up from the
+			 * subtree the fact that any <= ST_CLOSED was found and
+			 * set check accordingly for CHK_ORDER as below, but
+			 * still this is only an assertion....
+			 */
+			assert_node(child, nexcheck);
+			continue;
+		}
 		assert_node(child, check);
-		if (check == CHK_ORDER &&
-		    child->type != T_NEXUS &&
-		    child->state <= ST_CLOSED)
+		if (check == CHK_ORDER && child->state <= ST_CLOSED)
 			check = CHK_PEND;
 	}
 }