Initialize a variable in ldb to make code analysis tool happy
Initialize a variable in ldb to make code analysis tool happy

Summary: Closes https://github.com/facebook/rocksdb/pull/2529

Differential Revision: D5378787

Pulled By: siying

fbshipit-source-id: 801ecacc2804f77cb3c9e5e665829e439db68800

SunguckLee/RocksDB,bbiao/rocksdb,bbiao/rocksdb,Andymic/rocksdb,Andymic/rocksdb,SunguckLee/RocksDB,SunguckLee/RocksDB,SunguckLee/RocksDB,bbiao/rocksdb,SunguckLee/RocksDB,bbiao/rocksdb,bbiao/rocksdb,bbiao/rocksdb,SunguckLee/RocksDB,SunguckLee/RocksDB,Andymic/rocksdb,Andymic/rocksdb,Andymic/rocksdb,bbiao/rocksdb,Andymic/rocksdb,Andymic/rocksdb,bbiao/rocksdb,Andymic/rocksdb,SunguckLee/RocksDB