When downloading and running Bitcoin core for the first time, after clicking through the "Are you sure you want to open. it?" screen, there's a possibility that macOS will pass an argument like `-psn_0_SOME_ID` to the application, which results in a shutdown as it's an invalid argument:

![v0 19 0rc1 args shutdown](https://user-images.githubusercontent.com/863730/67034964-b026fc00-f0e6-11e9-8462-70d0fcf613e6.png)

This only happens on the first run, subsequent opens will work fine, but we should filter these out, otherwise it's a poor and confusing first experience.

{
    std::string datadir = gArgs.GetArg("-datadir", "");
    return datadir.empty() || fs::is_directory(fs::system_complete(datadir));
}
void ClearDatadirCache()
{
    LOCK(csPathCached);
    pathCached = fs::path();
    pathCachedNetSpecific = fs::path();
    g_blocks_path_cache_net_specific = fs::path();
}
fs::path GetConfigFile(const std::string& confPath)