Current master (73fc922ed64333d45f18d8a448f30cfa2ae0281e) crashes at the end of processing RPC `gettxoutsetinfo` on OS X:

```
$ ./bitcoind 
Assertion failed: (ok), function Next, file txdb.cpp, line 139.
Abort trap: 6
$ 
```

#include "txdb.h"
#include "chain.h"
#include "chainparams.h"
#include "hash.h"
#include "main.h"
#include "pow.h"
#include "uint256.h"
#include <stdint.h>
#include <boost/thread.hpp>
using namespace std;
static const char DB_COINS = 'c';
static const char DB_BLOCK_FILES = 'f';
static const char DB_TXINDEX = 't';
static const char DB_BLOCK_INDEX = 'b';
static const char DB_BEST_BLOCK = 'B';
static const char DB_FLAG = 'F';
static const char DB_REINDEX_FLAG = 'R';
static const char DB_LAST_BLOCK = 'l';
CCoinsViewDB::CCoinsViewDB(size_t nCacheSize, bool fMemory, bool fWipe) : db(GetDataDir() / "chainstate", nCacheSize, fMemory, fWipe, true) 
{
}
bool CCoinsViewDB::GetCoins(const uint256 &txid, CCoins &coins) const {
    return db.Read(make_pair(DB_COINS, txid), coins);
}
bool CCoinsViewDB::HaveCoins(const uint256 &txid) const {