fdo#39468 translated German comment in outdev.cxx

German comment about clipping backup translated in function
OutputDevice::ImplInitClipRegion().

Change-Id: I55c3b5899ae36a2e25204fd054b80bd786b17e91
Reviewed-on: https://gerrit.libreoffice.org/7966
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>