fix white space issue in hidden input

fix white space issue in hidden input

The calculated text size is used in atlas renderer.
When the text is all white space, partial render issue occurs because the width is 0.
To avoid issue, do not remove the white space size in hidden input mode.

Change-Id: Id92becdb0103fa6dee20c5cd272ee3d4314121c6
Signed-off-by: Bowon Ryu <bowon.ryu@samsung.com>