fixing division by 0, refs #1316

git-svn-id: http://svn.code.sf.net/p/sumo/code/trunk/sumo@16547 29f149b2-0c63-11e1-8f5c-a347f6a9acd0
fixing integer overflow, refs #1316

git-svn-id: http://svn.code.sf.net/p/sumo/code/trunk/sumo@16548 29f149b2-0c63-11e1-8f5c-a347f6a9acd0