Fix bug introduced by #690

[addreas]

Description

When the GetDashboards function is called for the re-sync it gets called with the namespace specified as the empty string, this wasn't accounted for in #690. So, after #690 the reconciliation of dashboards (for the periodic re-sync) started getting an empty list of known dashboards which then caused any checking of existing dashboards to fail.

Relevant issues/tickets

Some people have noticed that this started happening in 4.3.0 (myself included): #686 (comment)

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

• This change requires a documentation update
• I have added tests that prove my fix is effective or that my feature works
• I have added a test case that will be used to verify my changes
• Verified independently on a cluster by reviewer

Verification steps

Built and tested on my home cluster and seems to have solved the issue of new versions being created each sync period.
Docker image available here: ghcr.io/addreas/grafana-operator:v4.3.0-690-bugfix

[NissesSenap]

LGTM, thanks alot for helping out with this bug @addreas