Make shr-rescale-image respect get-buffer-window again

* lisp/net/shr.el (shr-rescale-image): Partially revert previous
change -- ressurrect the check for `get-buffer-window'.
1 job for master in 52 minutes and 6 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Test
failed #1776
test-all

00:52:06

 
Name Stage Failure
failed
test-all Test
Makefile:318: recipe for target 'check-doit' failed
make[2]: *** [check-doit] Error 1
make[1]: *** [check-expensive] Error 2
make: *** [check-expensive] Error 2
make[2]: Leaving directory '/builds/emacs/emacs/test'
Makefile:293: recipe for target 'check-expensive' failed
make[1]: Leaving directory '/builds/emacs/emacs/test'
Makefile:957: recipe for target 'check-expensive' failed
ERROR: Job failed: exit code 1