Fix issue for Preference.setSingleLineTitle() has no effect.

The flag to check whether the single line title attribute is initialized
only when we processed the layout attributes. When the attribute is not
set in the layout, but set through the setter method, the flag is not
being updated properly, and hence the title view is not set correctly.
Need to update the flag as well when the setter method is called.

Bug: 62947301
Test: manual
Change-Id: If843663165a0f3348048aaf1d920f3b740af5bc3