add error checking for non-existent users trying to log in

src/backend/database.py

@@ -1217,11 +1217,14 @@ class Database:
         Returns:
             bool: True if the login was successful, False if not
         """
+        try:
             salt = self.query_db(
                 "SELECT salt FROM user WHERE username=?", (user,), one=True
             )[0]
             if salt is None:
                 return False
+        except TypeError:
+            return False
         hashed_password = salt + hashed_password
         password = self.query_db(
             "SELECT password FROM user WHERE username=?", (user,), one=True