Fix memory leak warning in FwdLockEngine.cpp

If addValue does not succeed, there will be memory leak on
decodeSession. Fixed it by checking if addValue returns true first.

Plus fixed a small indentation error.

Test: mmm with static analyzer and warning disappears.
Change-Id: Ibf9b85e4c416e8fea8b80a3ba47f87f88573c54c