Fix EWW rendering of long RTL lines

* lisp/net/shr.el (shr-insert-document): Undo any previous hscroll
of the selected window before filling its lines.  (Bug#22250)

lisp/net/shr.el

@@ -246,6 +246,11 @@ DOM should be a parse tree as generated by
                                          (* (frame-char-width) 2)
                                        0)))))
         bidi-display-reordering)
+    ;; If the window was hscrolled for some reason, shr-fill-lines
+    ;; below will misbehave, because it silently assumes that it
+    ;; starts with a non-hscrolled window (vertical-motion will move
+    ;; to a wrong place otherwise).
+    (set-window-hscroll nil 0)
     (shr-descend dom)
     (shr-fill-lines start (point))
     (shr-remove-trailing-whitespace start (point))