Do not read certificate bundle from data dir by default

Before the resources/config/ca-bundle.crt was only used when the list of custom
certificates was empty and the instance was not installed. But it should also
be used when the list is empty and the instance is installed.

This is inverting the logic to stop if the instance is not installed to use the
default bundle. And it also does this when the list is empty.

Signed-off-by: Morris Jobke <hey@morrisjobke.de>