handle nil class error for linked_transaction in line.rb #168

calling  `super` before assigning value [] to `self.linked_transactions` is causing exception.

`super` calls `remove_linked_transactions` method which tries to delete previous `linked_transactions`. As `linked_transaction`  is not initialized yet so it generates 
`NoMethodError: undefined method 'delete_if' for nil:NilClass' ` exception. Initializing `linked_transaction` before `super` has fixed this exception