Dear Emacs maintainers,

I use shr to render HTML emails in Emacs.  As I prefer non-proportional 
fonts, I set

    (setq shr-use-fonts nil)

However, with some messages, Emacs started to use all system memory.  If 
shr-use-fonts is t, the rendering is fine.  Attached is a curated 
example triggering the bug: do

    (setq shr-use-fonts nil)
    select the whole html
    M-x shr-render-region

(I know the HTML is invalid but this is how the email message came.)

Best regards,
C.