fix merge-pdfs function

I tried writing a test around this, but I couldn't solve some major bugs with the save-as function. For one, it returns an empty PDF no matter what you write to it. This is because .close gets called on it first. But fixing that didn't solve the problem for some reason.

Also, create-pdf-helper puts the text into a map with :text as its key, but save-as doesn't appear to do anything with that. However, changing it use :lines [[{} text]] instead also didn't fix it.

So I'm kind of stumped there.

However, this does fix the problem of merge-pdfs just repeating the 2nd page over and over.