Fix force-sync not syncing when only a single source is configured.

[davidv1992]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 81.54%. Comparing base (3920d19) to head (77ab250).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
ntpd/src/force_sync/algorithm.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1742   +/-   ##
=======================================
  Coverage   81.54%   81.54%           
=======================================
  Files          64       64           
  Lines       20090    20090           
=======================================
  Hits        16382    16382           
  Misses       3708     3708           

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