get-text! in snip%

Like get-text in non-flattened mode, except that the characters are put into the given mutable string, instead of returned in a newly allocated string.

• (send a-snip get-text! buffer offset num buffer-offset) -> void
     buffer : mutable string
     offset : exact non-negative integer
     num : exact non-negative integer
     buffer-offset : exact non-negative integer

  The default implementation calls get-text, except in the case of a string-snip%, in which case buffer is filled directly. In either case, the buffer string is filled starting at position buffer-offset. The buffer string must be at least num + buffer-offset characters long.