STRPTR name = GetIconFormat(APTR handle);
HWEXT_ICON_FORMAT
extension bit has been set. See Extension plugins for details.
If that is the case, this function must return a null-terminated string
containing name of the format of the icon file handle passed in handle. The
string returned by this function can be retrieved from Hollywood scripts by
querying the #ATTRFORMAT attribute on the #ICON object type. The string you
return must be valid until FreeIcon() is called on the image handle
passed to this function.