added error handling to chapters if the wrong time format is used and no referrer is sent

chapters.py

@@ -11,7 +11,10 @@ def suggest_chapter(lectureid):
 		time= timedelta(hours=x.hour,minutes=x.minute,seconds=x.second).total_seconds()
 		time = int(time)
 	except ValueError:
+		if 'ref' in request.values:
 			flash('Falsches Zeitformat, "%H:%M:%S" wird erwartet. Z.B. "01:39:42" für eine Kapitel bei Stunde 1, Minute 39, Sekunde 42')
+			return redirect(request.values['ref'])
+		return 'Wrong time format, "%H:%M:%S" is expected',  400
 		
 	submitter = None
 	if not ismod():