Avoid creating formerly empty pages, that say they were moved.

wikibot.py

@@ -28,6 +28,8 @@ def move_page(old_pagename, new_pagename, delete=False):
     with Proxy(config.WIKI_API_URL) as proxy:
         # create new page with identical content #
         page_content = proxy.wiki.getPage(old_pagename)
+        if not page_content:
+            return
         proxy.wiki.putPage(new_pagename, page_content, {
                            "sum": "Moved from " + old_pagename})
         # update back links to new page