Explicitly check for Pathname
Explicitly check for Pathname

If the cover was html that included the Rails file path
(which is likely if it includes a wicked_pdf_*_helper),
this would incorrectly assume it to be a url or filename
instead of HTML content.
tinfoil/wicked_pdf,brendon/wicked_pdf,reenhanced/wicked_pdf,rubylogicgems/wicked_pdf,bonekost/wicked_pdf,yuhao900914/wicked_pdf,livetat/wicked_pdf,gogo52cn/wicked_pdf,yakjuly/wicked_pdf,xptavares/wicked_pdf,naveed-ahmad/wicked_pdf,mileszs/wicked_pdf,consolo/wicked_pdf