Backport -Wlogical-op fixes to 1.12.x
gcc 8 won't compile the dbus-1.12 branch, because new warnings have been added to
Note that this is a slight behaviour change. Previously, we accidentally accepted absolutely anything in a .service file section name, due to an unintended tautologous expression (which, if it had been written the way it was intended to be, would have excluded the only section name we actually use,
D-BUS Service (sic)). Now we apply the documented .desktop-style rules.
This change has been on master since 1.13.8 (December) without anyone reporting it causing problems.