bug#67764: 30.0.50; Opening image in eww no longer works

[john muhl]

In Emacs 29.1 the image opens as expected:

  emacs -Q
  M-: (eww "https://www.gnu.org/software/emacs/images/emacs.png";)

On master it fails with "Wrong type argument: stringp, nil".
Bisect says 4254544 is the first bad commit.


In GNU Emacs 30.0.50 (build 3, x86_64-pc-linux-gnu, GTK+ Version
 3.24.38, cairo version 1.18.0) of 2023-12-11 built on localhost
Repository revision: cd702556759b33662cd6536c89ef02ddcd93d4ff
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12302002
System Description: Fedora Linux 39 (Thirty Nine)

Configured using:
 'configure --with-native-compilation=no'

Configured features:
ACL CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GPM GSETTINGS
HARFBUZZ JPEG JSON LIBOTF LIBSELINUX LIBSYSTEMD LIBXML2 M17N_FLT
MODULES NOTIFY INOTIFY PDUMPER PNG RSVG SECCOMP SOUND SQLITE3
THREADS TIFF TOOLKIT_SCROLL_BARS TREE_SITTER WEBP X11 XDBE XIM
XINPUT2 XPM GTK3 ZLIB