libextractor: update to 1.19

libextractor: update to 1.19

1.15: fix potential 4 MB on-stack allocation / stack-based buffer overflow
in the OLE2 plugin.

1.16: security fix to not honour LIBEXTRACTOR_PREFIX when linked into a
SUID binary running as root; fix tIME chunk parser in PNG plugin, QT
mime-type detection, wrong constant in REAL plugin, multi-chunked
decompression in DEB plugin, GIF plugin memory leak, W32 IPC error
handling, gzip-compressed header bit-flags.

1.17: fix various minor issues, including a missing 0 terminator in ZIP
handling under particular circumstances.

1.18: detect secure execution mode properly when deciding whether to
honour LIBEXTRACTOR_PREFIX (use secure_getenv()/issetugid()/real vs
effective UID-GID instead of only checking for root).

1.19: add RTF and msoffice plugins; fix bugs and performance issues in
the unzip logic, an offset calculation issue in the WAV extractor, and
minor memory leaks in the ELF extractor; add OSS-Fuzz support.

Add the two new plugins to PLUGINS so they actually get built and
packaged rather than compiled and silently dropped. Per
src/plugins/Makefile.am upstream, neither needs a new dependency:
libextractor_rtf is unconditional (same group as the already-packaged
riff/ps plugins), and libextractor_msoffice only requires HAVE_ZLIB
(same group as the already-packaged deb/odf/zip plugins), which is
already satisfied.

Not build-verified: a pre-existing host python3/ncurses build failure
affecting every package in this feed blocks the build well before it
reaches libextractor's own compile step.

Signed-off-by: Daniel Golle <redacted>