Fix the test failure
Fix the test failure

Summary: AllocateFromHugePage() can return nullptr, and then we need to try to allocate the block with AllocateNewBlock()

Test Plan: arena_test

Reviewers: sdong

Reviewed By: sdong

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D47607

tsheasha/rocksdb,tsheasha/rocksdb,bbiao/rocksdb,wat-ze-hex/rocksdb,tsheasha/rocksdb,norton/rocksdb,hobinyoon/rocksdb,wat-ze-hex/rocksdb,wenduo/rocksdb,flabby/rocksdb,wenduo/rocksdb,SunguckLee/RocksDB,Vaisman/rocksdb,caijieming-baidu/rocksdb,ryneli/rocksdb,vmx/rocksdb,jalexanderqed/rocksdb,facebook/rocksdb,caijieming-baidu/rocksdb,Andymic/rocksdb,kaschaeffer/rocksdb,wat-ze-hex/rocksdb,SunguckLee/RocksDB,ryneli/rocksdb,Andymic/rocksdb,wenduo/rocksdb,biddyweb/rocksdb,OverlordQ/rocksdb,Vaisman/rocksdb,biddyweb/rocksdb,OverlordQ/rocksdb,flabby/rocksdb,flabby/rocksdb,bbiao/rocksdb,caijieming-baidu/rocksdb,OverlordQ/rocksdb,OverlordQ/rocksdb,wat-ze-hex/rocksdb,biddyweb/rocksdb,jalexanderqed/rocksdb,vmx/rocksdb,Andymic/rocksdb,ryneli/rocksdb,hobinyoon/rocksdb,norton/rocksdb,SunguckLee/RocksDB,bbiao/rocksdb,ryneli/rocksdb,OverlordQ/rocksdb,vmx/rocksdb,biddyweb/rocksdb,norton/rocksdb,flabby/rocksdb,Vaisman/rocksdb,kaschaeffer/rocksdb,jalexanderqed/rocksdb,Andymic/rocksdb,OverlordQ/rocksdb,norton/rocksdb,SunguckLee/RocksDB,hobinyoon/rocksdb,Vaisman/rocksdb,jalexanderqed/rocksdb,facebook/rocksdb,kaschaeffer/rocksdb,facebook/rocksdb,OverlordQ/rocksdb,wenduo/rocksdb,bbiao/rocksdb,SunguckLee/RocksDB,facebook/rocksdb,caijieming-baidu/rocksdb,bbiao/rocksdb,tsheasha/rocksdb,kaschaeffer/rocksdb,biddyweb/rocksdb,caijieming-baidu/rocksdb,flabby/rocksdb,Vaisman/rocksdb,vmx/rocksdb,bbiao/rocksdb,facebook/rocksdb,bbiao/rocksdb,Andymic/rocksdb,flabby/rocksdb,wat-ze-hex/rocksdb,wenduo/rocksdb,ryneli/rocksdb,SunguckLee/RocksDB,ryneli/rocksdb,jalexanderqed/rocksdb,hobinyoon/rocksdb,wat-ze-hex/rocksdb,bbiao/rocksdb,caijieming-baidu/rocksdb,jalexanderqed/rocksdb,tsheasha/rocksdb,tsheasha/rocksdb,tsheasha/rocksdb,wat-ze-hex/rocksdb,biddyweb/rocksdb,vmx/rocksdb,SunguckLee/RocksDB,SunguckLee/RocksDB,hobinyoon/rocksdb,facebook/rocksdb,vmx/rocksdb,hobinyoon/rocksdb,Andymic/rocksdb,norton/rocksdb,Andymic/rocksdb,jalexanderqed/rocksdb,norton/rocksdb,tsheasha/rocksdb,kaschaeffer/rocksdb,wenduo/rocksdb,norton/rocksdb,hobinyoon/rocksdb,hobinyoon/rocksdb,wenduo/rocksdb,biddyweb/rocksdb,flabby/rocksdb,kaschaeffer/rocksdb,vmx/rocksdb,wat-ze-hex/rocksdb,vmx/rocksdb,Vaisman/rocksdb,Andymic/rocksdb,Vaisman/rocksdb,ryneli/rocksdb,kaschaeffer/rocksdb,facebook/rocksdb,caijieming-baidu/rocksdb,norton/rocksdb,wenduo/rocksdb,facebook/rocksdb