project: `incus project get-current` is empty if you never switched the project

[mschiff]

Required information

• Distribution: Gentoo
• Distribution version: --
• The output of "incus info" or if that fails:
  • Incus version: 6.7

Issue description

The command incus project get-current should write the name of the current project to stdout which is the default project initially.

However, if you never used incus project switch command to switch to some project and then back to default, then the output of get-current is empty instead of default

Steps to reproduce

1. fresh installation
2. call incus project get-current -> no output!
3. create some new project: incus project create myproject
4. switch: incus project switch myproject
5. call incus project get-current -> "myproject"
6. switch back: incus project switch default
7. call incus project get-current -> "default"