Fix editing undo changes in eww fields

* eww.el (eww-tag-form): Don't overwrite initial form data in text
fields.
(eww-process-text-input): Make `M-t' at the end of text fields work
better (bug#19085).

lisp/net/eww.el

@@ -921,6 +921,7 @@ network, but just re-display the HTML already fetched."
   (let ((eww-form (list (cons :method (dom-attr dom 'method))
 			(cons :action (dom-attr dom 'action))))
 	(start (point)))
+    (insert "\n")
     (shr-ensure-paragraph)
     (shr-generic dom)
     (unless (bolp)
@@ -1030,6 +1031,7 @@ See URL `https://developer.mozilla.org/en-US/docs/Web/HTML/Element/Input'.")
 			(1- end)))))
     (let* ((form (get-text-property pos 'eww-form))
 	   (properties (text-properties-at pos))
+           (buffer-undo-list t)
 	   (inhibit-read-only t)
 	   (length (- end beg replace-length))
 	   (type (plist-get form :type)))
@@ -1050,13 +1052,13 @@ See URL `https://developer.mozilla.org/en-US/docs/Web/HTML/Element/Input'.")
 	 ((< length 0)
 	  ;; Add padding.
 	  (save-excursion
-	    (goto-char (1- end))
+	    (goto-char end)
 	    (goto-char
 	     (if (equal type "textarea")
 		 (1- (line-end-position))
 	       (1+ (eww-end-of-field))))
 	    (let ((start (point)))
-	      (insert (make-string (abs length) ? ))
+              (insert (make-string (abs length) ? ))
 	      (set-text-properties start (point) properties))
 	    (goto-char (1- end)))))
 	(set-text-properties (plist-get form :start) (plist-get form :end)
@@ -1070,8 +1072,9 @@ See URL `https://developer.mozilla.org/en-US/docs/Web/HTML/Element/Input'.")
 	  (when (equal type "password")
 	    ;; Display passwords as asterisks.
 	    (let ((start (eww-beginning-of-field)))
-	      (put-text-property start (+ start (length value))
-				 'display (make-string (length value) ?*)))))))))
+	      (put-text-property
+               start (+ start (length value))
+               'display (make-string (length value) ?*)))))))))
 
 (defun eww-tag-textarea (dom)
   (let ((start (point))