fix 'NSImage' may not respond to '-lockFocusFlipped:'

related commit: b3818f53812053e94196a58bbe474e2c3b72ac69

Change-Id: Ica27b3c2e474ebb85a69149e35021835f8183b69
Reviewed-on: https://gerrit.libreoffice.org/10011
Reviewed-by: Norbert Thiebaud <nthiebaud@gmail.com>
Tested-by: Norbert Thiebaud <nthiebaud@gmail.com>