Eliminate accessible name-changed event flood during initial load

Accessible name-changed events should not be emitted during the initial load of the icon container. They should only be emitted when a user-triggered action such as renaming the file causes the change.

This event is being emitted when the editable_text property is being set. During the initial load the value is null, so check for that condition and only emit the event when the original value is non-null.