Move post/comment ID boilerplate inside getters.

Borrows code from the upstream which has been working in production
reliably for ~months. Also, most of it was literally copy-pasted,
and the casted ID values aren't used later in the route functions.

files/helpers/jinja2.py

@@ -7,10 +7,6 @@ from files.helpers.assetcache import assetcache_path
 
 @app.template_filter("post_embed")
 def post_embed(id, v):
-
-	try: id = int(id)
-	except: return None
-	
 	p = get_post(id, v, graceful=True)
 	
 	if p: return render_template("submission_listing.html", listing=[p], v=v)