InvoicePrint leaks open files

org.adempiere.webui.process.PrintInvoice creates a single pdf from many single invoices (if more the one was generated), but leaves the single pdf files open.

The issue is caused by AEnv.mergePdf wich never closes the PdfReader it opens. They cannot be closed while looping becuause they are still needed when document.close() is called, but after that they can be closed.

See attached patch for a possible solution.

Regards,
Silvano, www.freepath.it