Fix "Acore" crash when exporting contacts to SDCard.

On Export confirmation (ExportConfirmationListener::onClick function)
start the ActualExportThread after the progress dialog window pop's up.
ActualExportThread::onCreateDialog instantiates ProgressDialog class,
the thread start (run) function access mProgressDialog methods.
since the thread started before the OnCreateDialog , the mProgressDialog
object is null , Hence the Exception is thrown.

Change-Id: Ia23e494535b7b7bd3066cbd418aff899c5e20825
CRs-Fixed:232123