message: refactor: Fix CAddrMan::Check style
  This change improves readability, and follows Developer Notes.
diff: @@ -716,10 +716,9 @@ private:
  void Check()
  {
  #ifdef DEBUG_ADDRMAN
  - {
  LOCK(cs);
  - int err;
  - if ((err=Check_()))
  + const int err = Check_();
  + if (err) {
  LogPrintf("ADDRMAN CONSISTENCY CHECK FAILED!!! err=%i\n", err);
  }
  #endif
  