Ignore invalid SVG images

* shr.el (shr-tag-svg): Ignore SVG images that have no width
or height, because these can't be displayed by ImageMagick,
anyway.

Backport:

(cherry picked from commit 821107d5)

lisp/net/shr.el

@@ -1152,7 +1152,9 @@ ones, in case fg and bg are nil."
 
 (defun shr-tag-svg (dom)
   (when (and (image-type-available-p 'svg)
-	     (not shr-inhibit-images))
+	     (not shr-inhibit-images)
+             (dom-attr dom 'width)
+             (dom-attr dom 'height))
     (funcall shr-put-image-function (list (shr-dom-to-xml dom) 'image/svg+xml)
 	     "SVG Image")))