mailDoc function is broken in JS (no attachment in email)

[sraka1]

In

pdfium/fxjs/cjs_document.cpp

Line 349 in 70c2db3

m_pFormFillEnv->JS_docmailForm(pdfium::span<const uint8_t>(), bUI, cTo,

it seems that an empty span is provided to the JS_docmailForm function (which is triggered by mailDoc from the JS context).

This results in the email client opening without the attachment, which is not in line with the Adobe spec.