- Move static undo variable into 'WriteData', 'memfile_chunk_add' used arguments in a confusing way, sometimes to set/clear static var. - Replace checks for 'wd->current' with 'wd->use_memfile' move memfile vars into 'wd->mem' struct.
- Move static undo variable into 'WriteData', 'memfile_chunk_add' used arguments in a confusing way, sometimes to set/clear static var. - Replace checks for 'wd->current' with 'wd->use_memfile' move memfile vars into 'wd->mem' struct.