Massive kmail breakage with mariadb-10.4.6

[Peter Humphrey]

Hello lists,

Yesterday's routine update took mariadb from 10.3.16 to 10.4.6. When I came to 
look at my emails today, kmail couldn't do anything. To start with, it was 
stuck in an endless, looping attempt to display the current email. Then it 
couldn't archive the inbox, then it couldn't import from an archive. I 
couldn't even move an email from one folder to another. Akonadictl fsck and 
vacuum seemed to run but didn't improve anything. Even reverting to an old 
copy of my home directory didn't help.

Eventually I noticed that mariadb had been upgraded, so I masked the latest 
version and reverted to the older one. Lo! and Behold! Kmail sprang back into 
life.

I've sent this to both the relevant lists; I hope that's not a heinous 
transgression.

-- 
Gentoo testing system
gcc 9.1.0, sys-kernel/gentoo-sources 5.1.12
QT 5.12.3, KDE frameworks 5.59.0, KDE plasma 5.16.1
KDE apps 19.04.2oo incl KMail 19.04.1-r1 (5.11.2), akonadi 19.04.0
x11-drivers/xf86-video-amdgpu 19.0.0
dev-libs/amdgpu-pro-opencl 18.20.684755