package/{mesa3d, mesa3d-headers}: bump version to 19.2.4

Quoting
https://lists.freedesktop.org/archives/mesa-announce/2019-November/000555.html


"This is an emergency release, to fix a critical bug found in the
 19.2.3 release which causes incomplete rendering on all mesa drivers."

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>