Int 2F Fn 4B04  - DOS 5+ Task Switcher - Free Switcher Id                  [T]

   AX = 4B04h
   BX = switcher ID
   ES:DI -> task switcher entry point (see AX=4B02h)

Return: AX = 0000h
   BX = status
       0000h successful
       other error (invalid ID or ID not allocated)

Notes: called by a task switcher when it exits, unless it was the first loaded
     and is providing the support for AX=4B03h and AX=4B04h
   the task switcher providing the identifiers may call the terminating
     task switcher's entry point as needed
   this call is available from within DOSSHELL even if the task switcher
     is not installed
   this call is supported by PC Tools v8+ CPTASK, but appears to return
     sucessfully no matter which ID is given

See Also: AX=4B02h,AX=4B03h