Fix preprocessor crash on small data sets without places

[GoogleCodeExporter]

Hi,

I just took a small snapshot of a few streets
and wanted to test some routing tweaks.

The trie writeout code omits the datalist size indicator
during Write() when both the label list and data list are empty.

This will result in an assertion since Read()
assumes there is a data list size indicator
if "labelist.size() <= 0".

Attached patch fixes the issue.

Cheers,
Thomas

PS: Your diploma thesis rocks! It really helped
me to understand how monav works.

Original issue reported on code.google.com by t...@simonv.com on 1 Jun 2013 at 9:52