fixed a bug in leaf node delete

Author: fuli

include/dos_tree.h

@@ -131,6 +131,11 @@ namespace alg
 				delete_case1(n);
 			}
 			replace_node(n, child);
+			// copy child value if exists
+			if (child != NULL) {
+				DOSNODE(n)->key = DOSNODE(child)->key;
+				DOSNODE(n)->size = DOSNODE(child)->size;
+			}
 			if (n->parent == NULL && child != NULL)
 				child->color = BLACK;