INT 15 - TopView - "ISOBJ" - VERIFY OBJECT HANDLE
        AX = 1016h
        ES:DI = possible object handle
Return: BX = FFFFh if ES:DI is a valid object handle
             0000h if ES:DI is not
Note:   under DESQview versions prior to 2.50, an object handle is always a
          pointer to the object; for versions 2.50 and up, only task handles
          are always pointers (other handles may consist of an object number
          and offset into DESQview's common memory)
SeeAlso: AX=DE2Bh

Format of object:
Offset  Size    Description
 00h    WORD    offset in common memory of previous object of same type
 02h    WORD    offset in common memory of next object of same type
 04h    WORD    signature FEDCh (DV 2.42-)
                signature FEDCh or object number (DV 2.50+)
 06h    WORD    object type
 08h    DWORD   object handle to return to caller
 0Ch    DWORD   canonicalized object address (segment = common memory)
        ...     varies by object type and DESQview version