fixed: grader crashes when the problem has no test data
fixed: grader crashes when the problem has no test data

git-svn-id: 0e7d180c1756de014b8f4d2a2c0b05a59909ba3f@431 6386c4cd-e34a-4fa8-8920-d93eb39b512e

nattee/cafe-grader-judge-scripts,jittat/cafe-grader-judge-scripts,nattee/cafe-grader-judge-scripts,nattee/cafe-grader-judge-scripts,jittat/cafe-grader-judge-scripts,jittat/cafe-grader-judge-scripts,nattee/cafe-grader-judge-scripts,jittat/cafe-grader-judge-scripts,nattee/cafe-grader-judge-scripts