ChangeLog: reference to 18625 actually corresponds to 18626

The ChangeLog lines:

    - Avoid spurious failures from configure files related to calling
      exit(0) in TOR_SEARCH_LIBRARY. Fixes bug 18625; bugfix on
      0.2.0.1-alpha. Patch from "cypherpunks".

actually correspond to #18626 (moved).

This issue was added in commit db13527.