[util.cpp#L216](https://github.com/bitcoin/bitcoin/blob/master/src/util.cpp#L216) 
if `fopen `failed, a null file pointer could be passed to `FileWriteStr(vMsgsBeforeOpenLog->front(), fileout);`
{
    assert(mutexDebugLog == NULL);
    mutexDebugLog = new boost::mutex();
    vMsgsBeforeOpenLog = new list<string>;
}
void OpenDebugLog()
{
    boost::call_once(&DebugPrintInit, debugPrintInitFlag);
    boost::mutex::scoped_lock scoped_lock(*mutexDebugLog);
    assert(fileout == NULL);
    assert(vMsgsBeforeOpenLog);
    boost::filesystem::path pathDebug = GetDataDir() / "debug.log";
    fileout = fopen(pathDebug.string().c_str(), "a");
    if (fileout) setbuf(fileout, NULL); 
    
    while (!vMsgsBeforeOpenLog->empty()) {
        FileWriteStr(vMsgsBeforeOpenLog->front(), fileout);
        vMsgsBeforeOpenLog->pop_front();
    }
    delete vMsgsBeforeOpenLog;
    vMsgsBeforeOpenLog = NULL;
}
bool LogAcceptCategory(const char* category)
{
    if (category != NULL)
    {
        if (!fDebug)