Handle optional slash in generic watch matcher

youtube-extract

@@ -80,7 +80,7 @@ videoPattern = '|'.join([
 	r'/www\.youtube\.com/(my_videos_)?edit\?(.*&)?video_id=[0-9A-Za-z_-]{11}',
 	r'/www\.youtube\.com/(all_comments|attribution|cthru|get_endscreen|livestreaming/dashboard)\?(.*&)?v=[0-9A-Za-z_-]{11}',
 	# Generic v parameter on watch URLs including with percent encoding; this covers e.g. google.com/url?... or the oEmbed
-	r'/watch\?(.*&)?v=[0-9A-Za-z_-]{11}',
+	r'/watch/?\?(.*&)?v=[0-9A-Za-z_-]{11}',
   ])