In case of empty values , the accelerator character is passed as the button name which avoids extra spacing.

Change-Id: I8a82f5226e17bf8977fb6a8fd59c99a244e59309
Reviewed-on: https://gerrit.libreoffice.org/14498Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Norbert Thiebaud <nthiebaud@gmail.com>