[vz-dev] [volkszaehler/vzlogger] b00108: add mutex lock for logging. (#406)

[magicWF]

  Branch: refs/heads/master
  Home:   https://github.com/volkszaehler/vzlogger
  Commit: b00108848b27dc295fdaa56321c6c78db9c81828
      https://github.com/volkszaehler/vzlogger/commit/b00108848b27dc295fdaa56321c6c78db9c81828
  Author: magicWF <magicWF at users.noreply.github.com>
  Date:   2019-12-15 (Sun, 15 Dec 2019)

  Changed paths:
    M src/vzlogger.cpp

  Log Message:
  -----------
  add mutex lock for logging. (#406)

* add mutex lock for logging.

* correct typo in unlock function call.

* Mutex is closer to the function calls to be protected.