Core: Fix CoreDFB::GetSurface(Buffer) for single app builds.
Core: Fix CoreDFB::GetSurface(Buffer) for single app builds.

deniskropp/DirectFB,djbclark/directfb-core-DirectFB,lancebaiyouview/DirectFB,jcdubois/DirectFB,sklnet/DirectFB,deniskropp/DirectFB,lancebaiyouview/DirectFB,djbclark/directfb-core-DirectFB,lancebaiyouview/DirectFB,jcdubois/DirectFB,kaostao/directfb,lancebaiyouview/DirectFB,sklnet/DirectFB,jcdubois/DirectFB,deniskropp/DirectFB,djbclark/directfb-core-DirectFB,kaostao/directfb,djbclark/directfb-core-DirectFB,sklnet/DirectFB,sklnet/DirectFB,deniskropp/DirectFB,kaostao/directfb