Add NULL check during restoreVM operation when host is removed

[nvazquez]

Description

This PR addresses a fix for the following use case:

• Create VM
• Start VM
• Stop VM
• Delete Host where VM was started
• Restore VM -> Restore VM command failed, VM ended up with two ROOT volumes, one of them is in Allocated state
• Expected result: VM restored (with new template)

Types of changes

• Breaking change (fix or feature that would cause existing functionality to change)
• New feature (non-breaking change which adds functionality)
• Bug fix (non-breaking change which fixes an issue)
• Enhancement (improves an existing feature and functionality)
• Cleanup (Code refactoring and cleanup, that may add test cases)
• Build/CI
• Test (unit or integration test code)

Feature/Enhancement Scale or Bug Severity

Feature/Enhancement Scale

• Major
• Minor

Bug Severity

• BLOCKER
• Critical
• Major
• Minor
• Trivial

Screenshots (if appropriate):

How Has This Been Tested?

How did you try to break this feature and the system with this change?