DynamoDS/Dynamo — pull request #2814 by ke-yu (2014-10-21 05:18:35+00:00)
Title: Fix range expression defect MAGN-5111

This pull request fixes [MAGN-5111: Crash when step range expression come to infinity.](http://adsk-oss.myjetbrains.com/youtrack/issue/MAGN-5111)

Add more validity checks.

@aparajit-pratap please help to review the change.