Draft: Ensure file buffer freed if in system mode
Commit 2788f039 made freeing of the file buffer sensitive to processor mode. It checked the mode and, according to the narrative, only freed the system file buffer if in system mode, but the check selected user mode. The consequence of this was that 4k of ram was lost irretrievably on every file close (fclose) in system mode, leading to a potentially horrendous leak. This mod corrects that such that the system (owned) file buf will only be freed if in system mode. It is possible this breaks the intent of the initial fix, but the leak of memoryneeds to be fixed.