upgrade to jpeg-9a

Includes some type conversion fixes.

Change-Id: I84f886e9f922acd780d46baea97f2d87c5ac700b
Reviewed-on: https://gerrit.libreoffice.org/9306
Tested-by: LibreOffice gerrit bot <gerrit@libreoffice.org>
Reviewed-by: Thomas Arnhold <thomas@arnhold.org>
Tested-by: Thomas Arnhold <thomas@arnhold.org>