Fix issue where size of map is 2 less than actual size

The border (invisible) grids are not accounted. The map size in the XML needs
these border grids to be accounted for.
Fix issue where NullPointerException happens when parsing XML

This issue is caused because most border grids are not stated in the XML file.
This is fixed by initializing all the grids to NON_ROAD before attempting to
read the file.
Fix missing node in XML

The <cars> tag is missing.