Fix KBOSS backup creation edge case

[JoaoJandre]

Description

If a new incremental backup is created for a stopped VM, that has a delta tree with more than one branch for one of its volumes, and the VM snapshot following the last backup is the current one, a problem occurs during backup creation where the current VM snapshot delta is not rebased to its new parent, causing subsequent backups to fail and the chain to become inconsistent.

This PR fixes this issue.

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?

Test description

With a stopped VM, the following tests were performed:

Test	Previous result	Result with patch
Take a backup, a VM snapshot, and a new backup	Success and consistent chain	Success and consistent chain
Take a backup, two consecutive VM snapshots, revert to the first VM snapshot, take a new VM snapshot, and then take a new backup	Success and consistent chain	Success and consistent chain
Take a backup, two consecutive VM snapshots, revert to the first VM snapshot, and then take a new backup	Success, but the chain becomes inconsistent, making it impossible to start the VM	Success and consistent chain

[JoaoJandre]

@winterhazel if we have a new RC could we include this?
Otherwise, this can go to the next minor.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 3.41%. Comparing base (dbee809) to head (14f9086).

❗ There is a different number of reports uploaded between BASE (dbee809) and HEAD (14f9086). Click for more details.

HEAD has 1 upload less than BASE

Flag	BASE (dbee809)	HEAD (14f9086)
unittests	1	0

Additional details and impacted files

@@              Coverage Diff              @@
##               main   #13880       +/-   ##
=============================================
- Coverage     19.64%    3.41%   -16.24%     
=============================================
  Files          6368      487     -5881     
  Lines        574889    41867   -533022     
  Branches      70353     7912    -62441     
=============================================
- Hits         112935     1429   -111506     
+ Misses       449684    40238   -409446     
+ Partials      12270      200    -12070     

Flag	Coverage Δ
uitests	3.41% <ø> (ø)
unittests	?

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