MAHOUT-1367: Exception in thread "main" java.lang.NullPointerException, caused by not validating the input path.

git-svn-id: https://svn.apache.org/repos/asf/mahout/trunk@1546806 13f79535-47bb-0310-9956-ffa450edef68
MAHOUT-1367: WikipediaXmlSplitter --> Exception in thread main java.lang.NullPointerException

git-svn-id: https://svn.apache.org/repos/asf/mahout/trunk@1546807 13f79535-47bb-0310-9956-ffa450edef68