bug#34138: 27.0.50; Delayed display of PDF file images

[Stephen Berman]

Since a recent commit, I'm seeing a delay in the display of PDF files as
images (both with -Q and with my initializations).  I see this in both
doc-view-mode and pdf-view-mode (from the pdf-tools package, available
from MELPA).  In doc-view-mode, on visiting a PDF file, it at first
appears as raw PDF, as when visiting it in fundamental-mode, and only
after a few seconds does the image appear.  The same happens in
pdf-view-mode but there the delay is much longer -- with some files it
takes close to a minute on my machine before the image is displayed,
unless I provide keyboard input, which makes the image appear
immediately.  In addition, in pdf-view-mode this appears in *Message*:
Error during redisplay: (eval (pdf-misc-size-indication)) signaled
(error "Invalid image specification: nil").  In doc-view-mode there is
no such error message.  Git bisect pinpoints this commit:

e567ac1495..: Martin Rudalics 2019-01-11 Run window change functions
during redisplay


In GNU Emacs 27.0.50 (build 26, x86_64-pc-linux-gnu, GTK+ Version 3.22.30)
 of 2019-01-19 built on rosalinde
Repository revision: b821a70cb9467186afb55734a0e5cb4601909916
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12001000
System Description: 8.3

Configured using:
 'configure 'CFLAGS=-Og -g3''

Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND DBUS GSETTINGS GLIB NOTIFY
INOTIFY ACL GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB
TOOLKIT_SCROLL_BARS GTK3 X11 XDBE XIM THREADS CANNOT_DUMP LCMS2 GMP

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