[TASK] Update adodb to v5.20.3

This brings a list of bug fixes and better PHP7 compatibility.
This is a "hacked" version from vanilla 5.20.3 where some
local changes are applied that were not yet fixed upstream,
see forge for a diff.

Change-Id: I16a3d601bc0b1bf77ab3bd35311a57df6595a1ed
Resolves: #75447
Releases: master, 7.6
Reviewed-on: https://review.typo3.org/47537


Reviewed-by: Daniel Goerz <ervaude@gmail.com>
Reviewed-by: Frank Naegler <frank.naegler@typo3.org>
Tested-by: Frank Naegler <frank.naegler@typo3.org>
Reviewed-by: Morton Jonuschat <m.jonuschat@mojocode.de>
Tested-by: Morton Jonuschat <m.jonuschat@mojocode.de>