[SPARK-7615][MLLIB] MLLIB Word2Vec wordVectors divided by Euclidean Norm equals to zero

Cosine similarity with 0 vector should be 0

Related to https://github.com/apache/spark/pull/10152

Author: Sean Owen <sowen@cloudera.com>

Closes #10696 from srowen/SPARK-7615.

mllib/src/main/scala/org/apache/spark/mllib/feature/Word2Vec.scala

@@ -543,7 +543,12 @@ class Word2VecModel private[spark] (
     val cosVec = cosineVec.map(_.toDouble)
     var ind = 0
     while (ind < numWords) {
-      cosVec(ind) /= wordVecNorms(ind)
+      val norm = wordVecNorms(ind)
+      if (norm == 0.0) {
+        cosVec(ind) = 0.0
+      } else {
+        cosVec(ind) /= norm
+      }
       ind += 1
     }
     wordList.zip(cosVec)