fix wrong behaviour of SelectWholeText()

fix wrong behaviour of SelectWholeText()

When there are multiple text controls,
there is a problem that the selection is keeped even if the text control loses focus
due to another text control's SelectWholeText().

This patch prevents wrong selection updates via flags.

// example
DevelTextField::SelectWholeText(field1);
DevelTextField::SelectWholeText(field2);
DevelTextField::SelectWholeText(field3);
DevelTextField::SelectWholeText(field4);

In the case of above example, all TextFields display a selection.

Change-Id: I96f87d0b12e4a91493831ca55e0f8b662391456e
Signed-off-by: Bowon Ryu <bowon.ryu@samsung.com>