Fix a bug on assigning magic number to file structure
Fix a bug on assigning magic number to file structure

- This bug sporadically causes unexpected failure.

Change-Id: I587c2bda6b262e07178df51d6c8bd90fec1832a1

wurikiji/forestdb,couchbase/forestdb,couchbase/forestdb,hisundar/forestdb,wurikiji/forestdb,hisundar/forestdb