Fix problem with spurious extra paragraphs in shr

* lisp/net/shr.el (shr-ensure-paragraph): Don't regard <div
id=foo></div> (empty placeholders) as occupying any space (bug#43510).

lisp/net/shr.el

@@ -555,7 +555,7 @@ size, and full-buffer size."
 	  ;; If the element was empty, we don't have anything to put the
 	  ;; anchor on.  So just insert a dummy character.
 	  (when (= start (point))
-            (insert ?*)
+            (insert ? )
             (put-text-property (1- (point)) (point) 'display ""))
           (put-text-property start (1+ start) 'shr-target-id id))
 	;; If style is set, then this node has set the color.
@@ -932,6 +932,22 @@ size, and full-buffer size."
 	       (looking-at " *$")))
 	;; We're already at a new paragraph; do nothing.
 	)
+       ((and (not (bolp))
+             (save-excursion
+               (beginning-of-line)
+               (looking-at " *$"))
+	     (save-excursion
+	       (forward-line -1)
+	       (looking-at " *$"))
+             ;; Check all chars on the current line and see whether
+             ;; they're all placeholders.
+             (cl-loop for pos from (line-beginning-position) upto (1- (point))
+                      unless (get-text-property pos 'shr-target-id)
+                      return nil
+                      finally return t))
+	;; We have some invisible markers from <div id="foo"></div>;
+	;; do nothing.
+	)
        ((and prefix
 	     (= prefix (- (point) (line-beginning-position))))
 	;; Do nothing; we're at the start of a <li>.