Fix exception when trying to register existing user

db/sqlite.py

@@ -51,8 +51,10 @@ class DB:
         ).fetchone()
         comments = db.execute('''
             select comment_id, parent_id, author_id, name, text, create_time, modify_time
-            from comments, users
-            where thread_id = ? and author_id = user_id
+            from comments
+              left join users
+              on author_id = user_id
+            where thread_id = ?
             ''',
             (thread,)
         )
@@ -293,6 +295,7 @@ class DB:
         return False
 
     def add_user(self, username, password, time):
+        try:
             db = self._db()
             c = db.cursor()
             c.execute('''
@@ -305,6 +308,9 @@ class DB:
                 db.commit()
                 return True
             return False
+        except sqlite3.IntegrityError:
+            # User already exists, probably
+            return False
 
     def _db(self):
         return sqlite3.connect(self.conn)

main.py

@@ -274,7 +274,7 @@ def register():
         ):
             flash('CAPTCHA answer is incorrect', 'error')
         elif not db.add_user(username, hash_password(password), time.time_ns()):
-            flash('Failed to create user (username may already be taken)')
+            flash('Failed to create account (username may already be taken)', 'error')
         else:
             flash('Account has been created. You can login now.', 'success')
             return redirect(url_for('index'))