Fix getting node by field name or ID.

lib/src/node.c

@@ -564,7 +564,10 @@ recur:
       // If the field refers to a hidden node, return its first visible
       // child.
       else {
-        return ts_node_child(child, 0);
+        TSNode result = ts_node_child(child, 0);
+        if (result.id) return result;
+        field_map++;
+        if (field_map == field_map_end) return ts_node__null();
       }
     }
   }