GitLab

Detail:
  Summary of how non-CnP Wimp treats the window handle for Wimp_SetCaretPosition
  R0 = valid window handle
    or invalid window handle (mapped to -1)
    or any negative number or 0 (mapped to -1)

  With this change, the CnP Wimp does
  R0 = valid window handle
    or invalid window handle (throws error)
    or any negative number or 0 if pre RISC OS 5 (mapped to -1)
    or 0 for RISC OS 5 (mapped to -1)

  Noting the use of AcceptLoosePointer macro if built for a 26 bit target.