fix #591 invalid local filename when content-disposition invalid extension

1. fix download to remove query string from attachment name
   can cause regressions when filename contains query before extension
   or other strange characters because we parse as url an intended filename
2. fix episode.local_filename() to always sanitize the extension

src/gpodder/download.py

@@ -821,7 +821,10 @@ class DownloadTask(object):
             # an empty filename, resulting in an empty string here (bug 1440)
             if disposition_filename is not None and disposition_filename != '':
                 # The server specifies a download filename - try to use it
-                disposition_filename = os.path.basename(disposition_filename)
+                # filename_from_url to remove query string; see #591
+                fn, ext = util.filename_from_url(disposition_filename)
+                logger.debug("converting disposition filename '%s' to local filename '%s%s'", disposition_filename, fn, ext)
+                disposition_filename = fn + ext
                 self.filename = self.__episode.local_filename(create=True,
                         force_update=True, template=disposition_filename)
                 new_mimetype, encoding = mimetypes.guess_type(self.filename)

src/gpodder/model.py

@@ -471,6 +471,8 @@ class PodcastEpisode(PodcastModelObject):
                         self.channel.url, self.url)
                 fn_template = hashlib.md5(self.url.encode('utf-8')).hexdigest()
 
+            # Also sanitize ext (see #591 where ext=.mp3?dest-id=754182)
+            ext = '.' + util.sanitize_filename(ext, self.MAX_FILENAME_LENGTH - len(fn_template) - 1)
             # Find a unique filename for this episode
             wanted_filename = self.find_unique_file_name(fn_template, ext)