[SPARK-12765][ML][COUNTVECTORIZER] fix CountVectorizer.transform's lost transformSchema

https://issues.apache.org/jira/browse/SPARK-12765

Author: Liu Xiang <lxmtlab@gmail.com>

Closes #10720 from sloth2012/sloth.

mllib/src/main/scala/org/apache/spark/ml/feature/CountVectorizer.scala

@@ -210,6 +210,7 @@ class CountVectorizerModel(override val uid: String, val vocabulary: Array[Strin
   private var broadcastDict: Option[Broadcast[Map[String, Int]]] = None
 
   override def transform(dataset: DataFrame): DataFrame = {
+    transformSchema(dataset.schema, logging = true)
     if (broadcastDict.isEmpty) {
       val dict = vocabulary.zipWithIndex.toMap
       broadcastDict = Some(dataset.sqlContext.sparkContext.broadcast(dict))