[client] Fix a panic on shutdown if dns host manager failed to initialize

[lixmal]

Describe your changes

If the inner host manager init fails, we will be left with a non-nil s.hostManager despite the inner value being nil. Any s.hostManager != nil check will pass, but method calls on this struct will panic.

Issue ticket number and link

Checklist

• Is it a bug fix
• Is a typo/documentation fix
• Is a feature enhancement
• It is a refactor
• Created tests that fail without the change (if possible)
• Extended the README / documentation, if necessary

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

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