[FIX] website_slides: allow upload of >20MB files (as limit is 25MB)

There is a double-check (on client and on server) to prevent the user to
upload a >25 MB document. The client checks the actual file size while
the server guesses it from the total received payload. This server guess
is wrong as the extra payload is quite huge (5-10MB). Now the server
checks the real file size as it should have from the beginning.

addons/website_slides/controllers/main.py

@@ -292,10 +292,8 @@ class website_slides(http.Controller):
 
     @http.route(['/slides/add_slide'], type='json', auth='user', methods=['POST'], website=True)
     def create_slide(self, *args, **post):
-        payload = request.httprequest.content_length
-        # payload is total request content size so it's not exact size of file.
-        # already add client validation this is for double check if client alter.
-        if (payload / 1024 / 1024 > 25):
+        file_size = len(post['datas']) * 3 / 4; # base64
+        if (file_size / 1024.0 / 1024.0) > 25:
             return {'error': _('File is too big. File size cannot exceed 25MB')}
 
         values = dict((fname, post[fname]) for fname in [