koGrid doesn't set checkbox properly -with code fix

When trying to set checkbox the toggleSelected return undefined value, stopping the check event chain and thereby isn't the checkbox "visually set".

Fix for my particular problem was to make the following change (line 1109)

from: afterSelectionChange: function () { },
to: afterSelectionChange: function () { return true; },

since the return statement on line 1633:
return self.afterSelectionChange(self, event);
returns undefined without the "fix" and causing the mentioned problem.

Start at the callback definition around line 1109 and trace the call and return at line 1633. Verify the checkbox selection event and its visual state, then confirm the change with the relevant existing behavior or tests; done means the checkbox is visibly set without stopping the event chain.

Written by the indexing model from the issue text.