trebuchet: build headers from internal adapter instance

Trebuchet will be killed if any of its settings changed, so if it is accessed from recents
then the PreferencesActivity is rebuilt from its saved instance and the headers are not filled
by onBuildHeaders, because this is not called.
Just ensure we build the headers from the internal adapter.

Change-Id: I3159daadd715d5cbc0d9bcd377d8bbe51f638d32
Signed-off-by: Jorge Ruesga <jorge@ruesga.com>
Merge "trebuchet: build headers from internal adapter instance" into cm-11.0