fdo#73466 SwTxtSizeInfo / SwTxtInputFldPortion: invalid string access

Change-Id: Ibd74e3b0cd45fa3bf6fd4135866b22acd16e372e
(cherry picked from commit fc0bd38051c7c8f4c68a1407aed32a96b2564510)
Signed-off-by: Andras Timar <andras.timar@collabora.com>