同意网友的看法。句子中的不定式改用完成式更合适，因为是针对“已经找到它”的人，而不是“要找到它”的人。体会下面用不定式完成式的句子：

I happened to have heard it. 我碰巧听见了这事。

He happened to have heard of the book. 他碰巧听人说起过这本书。

I happened to have driven that kind of car before. 我碰巧过去曾开过那种汽车。

比较下面用不定式一般式的句子：

If you happened to be in town, would you ask about it? 你要是有机会进城，可不可以问问这件事？

If they happened to offer you the job, would you accept? 如果他们给你这份工作，你会接受吗?

If we happened to brush carelessly against the over-hanging rocks they would crash down at any moment. 如果我们不小心偶然碰着那些悬空的岩石，它们随时都可能掉下来。