COMBO: Fix bug that the select function is not apply

COMBO: Fix bug that the select function is not apply

When user call the select(), the select() is calling the setText()
and, the setText() is calling the listener(SWT.Modify) of the user because change text.
but, when the user call getSelectionIndex() in the listener(SWT.Modify) of user,
the selection index has not yet been reflected.
So, first call to select() before the setText() is called.

Change-Id: Ib1f8762d13d4fb09ccae2ee76ad0689f901cb6a6
Signed-off-by: HyunJong Park <paulhj.park@samsung.com>