With large "max_playlist_length" settings, the "data" array can be
very large, and initializing it during MPD startup causes page faults,
resulting in allocation of physical RAM.  This commit postpones the
initialization until the queue is really large, to avoid wasting
memory.

The former was deprecated with C++14.

According to the C++11 and C++17 standards, both files are identical.
Signed-off-by: Rosen Penev <rosenp@gmail.com>