bug#28503: 25.3; buffer-file-name returns nil in eww-pdfs

[Alex Branham]

>From emacs -Q:

M-x eww
(navigate to a pdf, I found this by searching "pdf test page"): 
http://www.orimi.com/pdf-test.pdf

then eval (buffer-file-name)

For me, it returns nil even though the pdf is a file on my computer (somewhere 
in /tmp for me).

It would be nice if this returned the actual path; I am trying to write a 
different function that will copy the pdf file elsewhere on my computer.

Thanks!


In GNU Emacs 25.3.1 (x86_64-pc-linux-gnu, GTK+ Version 3.22.19)
 of 2017-09-16 built on juergen
Windowing system distributor 'The X.Org Foundation', version 11.0.11903000
Configured using:
 'configure --prefix=/usr --sysconfdir=/etc --libexecdir=/usr/lib
 --localstatedir=/var --with-x-toolkit=gtk3 --with-xft --with-modules
 'CFLAGS=-march=x86-64 -mtune=generic -O2 -pipe -fstack-protector-strong
 -fno-plt' CPPFLAGS=-D_FORTIFY_SOURCE=2
 LDFLAGS=-Wl,-O1,--sort-common,--as-needed,-z,relro,-z,now'

Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND GPM DBUS GCONF GSETTINGS
NOTIFY ACL GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB
TOOLKIT_SCROLL_BARS GTK3 X11 MODULES

Important settings:
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

Major mode: eww