Non-cached calls to xdgRuntimeDirectory use wrong env. variable

[Ed Bruck]

xdgRuntimeDirectory uses wrong environment variable when called with a null handle. My understanding is that it should use XDG_RUNTIME_DIR instead of XDG_RUNTIME_DIRECTORY:

const char * xdgRuntimeDirectory(xdgHandle *handle)
{
    if (handle)
        return xdgGetCache(handle)->runtimeDirectory;
    else
        return xdgEnvDup("XDG_RUNTIME_DIRECTORY");
}

Calling with NULL returns a NULL pointer, because XDG_RUNTIME_DIRECTORY does not exist.