gsed: update to 4.9.

* Noteworthy changes in release 4.9 (2022-11-06) [stable]

** Bug fixes

  'sed --follow-symlinks -i' no longer loops forever when its operand
  is a symbolic link cycle.
  [bug introduced in sed 4.2]

  a program with an execution line longer than 2GB can no longer trigger
  an out-of-bounds memory write.

  using the R command to read an input line of length longer than 2GB
  can no longer trigger an out-of-bounds memory read.

  In locales using UTF-8 encoding, the regular expression '.' no
  longer sometimes fails to match Unicode characters U+D400 through
  U+D7FF (some Hangul Syllables, and Hangul Jamo Extended-B) and
  Unicode characters U+108000 through U+10FFFF (half of Supplemental
  Private Use Area plane B).
  [bug introduced in sed 4.8]

  I/O errors involving temp files no longer confuse sed into using a
  FILE * pointer after fclosing it, which has undefined behavior in C.

** New Features

  The 'r' command now accepts address 0, allowing inserting a file before
  the first line.

** Changes in behavior

  Sed now prints the less-surprising variant in a corner case of
  POSIX-unspecified behavior.  Before, this would print "n".
  Now, it prints "X":

    printf n | sed 'sn\nnXn'; echo

(wiz)