"Exclude gaps" option is not taken into account if it was changed during distance matrix calculation

Scenario to reproduce:

1. Open an alignment.
2. Open "Statistics" options panel tab.
3. Set any sequence as reference.
4. Turn on "Show distances column" option.
   Expected state: a calculation task is launched.
5. After the task finish quickly click two times to the "Exclude gaps" checkbox.
   Expected state: after all tasks finish distances are the same as in the previous step.
   Current state: the distances are not the same.