database: account for newmode in directory preparation

The commit a6736532 (database: implement uvol support) switched from using newmode to always using dir->mode when creating non-existent directories, making newmode an unused argument.

As far as I can see this is probably an oversight and may result in incorrect directory permissions, as we've been seeing in the #10952 (closed) issue; this is however not confirmed.

This restores the prior behavior.