aur-repo: set db_root from pacman.conf
aur-repo: set db_root from pacman.conf

7c6486015a4d377406e4cebff92f2b43cab27fbd removed setting db_root from
pacman.conf if db_name was not set, in the assumption that db_root would
be set in the pacman-conf loop. However, latter is only done if db_name
is specified with -d. Revert this commit.

Fixes #795

AladW/aurutils,AladW/aurutils