Fix separator for comments

Patch was the wrong way around. *omg*

Just realized, that it's just removing the trailing separator, but not the separator(s) between slots. Please consider this new patch, which first unsets all empty comments and then joins the remaining ones together.

I have an error "Error: Call to a member function __toString() on string in Drupal\office_hours\Plugin\Field\FieldType\OfficeHoursItemList->formatSlots() "
Also sometimes, $item can be NULL.

I committed a slightly different patch. Thanks.

Automatically closed - issue fixed for 2 weeks with no activity.