Clears warning from gcc 11.2:

saveutil.c: In function ‘WriteSave’:
saveutil.c:315:75: warning: ‘%s’ directive output may be truncated
 writing up to 1023 bytes into a region of size 221 [-Wformat-truncation=]
  315 |         snprintf (msg, sizeof(msg), "%s: Error creating session save file %s",
      |                                                                           ^~
  316 |                   Argv[0], session_save_file);
      |                            ~~~~~~~~~~~~~~~~~
saveutil.c:315:9: note: ‘snprintf’ output 36 or more bytes (assuming 1059)
 into a destination of size 256
  315 |         snprintf (msg, sizeof(msg), "%s: Error creating session save file %s",
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  316 |                   Argv[0], session_save_file);
      |                   ~~~~~~~~~~~~~~~~~~~~~~~~~~~

Signed-off-by: Alan Coopersmith <alan.coopersmith@oracle.com>