[dbnode] Fix setting of Head/Tail finalize flags for Segment

[linasm]

What this PR does / why we need it: In some cases Segment.Flags was being set to FinalizeHead&FinalizeTail which was clearly not intended because this expression results in 0 with the consequence of neither Head nor Tail being finalized during Segment.Finalize(). Fixed by changing the expression to FinalizeHead|FinalizeTail which results in finalizing both Head and Tail.

Special notes for your reviewer: Somewhat worried that introducing finalization where it belongs might cause a double finalize in case there was some other code finalizing Segment.Head or Segment.Tail. Inspecting via IDE did not reveal any such cases directly.

Does this PR introduce a user-facing and/or backwards incompatible change?: NONE

Does this PR require updating code package or user-facing documentation?: NONE

[codecov[bot]]

Codecov Report

Merging #2648 (1ae14df) into master (6e56231) will increase coverage by 14.4%. The diff coverage is 100.0%.

:exclamation: Current head 1ae14df differs from pull request most recent head ef3e68e. Consider uploading reports for the commit ef3e68e to get more accurate results

Additional details and impacted files

@@            Coverage Diff            @@
##           master   #2648      +/-   ##
=========================================
+ Coverage    57.3%   71.7%   +14.4%     
=========================================
  Files         553    1086     +533     
  Lines       63161   96909   +33748     
=========================================
+ Hits        36227   69566   +33339     
+ Misses      23729   22650    -1079     
- Partials     3205    4693    +1488     

Flag	Coverage Δ
aggregator	76.0% <ø> (+13.4%)	:arrow_up:
cluster	85.0% <ø> (∅)
collector	82.8% <ø> (?)
dbnode	79.3% <100.0%> (+17.8%)	:arrow_up:
m3em	74.4% <ø> (+27.9%)	:arrow_up:
m3ninx	72.2% <ø> (?)
m3nsch	51.1% <ø> (?)
metrics	17.2% <ø> (-2.4%)	:arrow_down:
msg	73.7% <ø> (-0.8%)	:arrow_down:
query	68.0% <ø> (?)
x	80.8% <ø> (?)

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