initialize many attributes that could have been left without init value

initialize many attributes that could have been left without init value

done with clang-tidy

run-clang-tidy -p build -config="{Checks: '*', CheckOptions: [{key: UseAssignment, value: true}]}" -checks='-*,cppcoreguidelines-pro-type-member-init' -fix

Signed-off-by: Matthieu Gallien <matthieu.gallien@nextcloud.com>