osl_getVolumeInformation: only stat if necessary
osl_getVolumeInformation: only stat if necessary

...in the hope that that makes cid#706206 (TOCTOU) go away

Change-Id: I4bc7b44e0268cf5d46aaf55fb4073dcdf67b324c

JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core