[SPARK-13537][SQL] Fix readBytes in VectorizedPlainValuesReader

JIRA: https://issues.apache.org/jira/browse/SPARK-13537

## What changes were proposed in this pull request?

In readBytes of VectorizedPlainValuesReader, we use buffer[offset] to access bytes in buffer. It is incorrect because offset is added with Platform.BYTE_ARRAY_OFFSET when initialization. We should fix it.

## How was this patch tested?

`ParquetHadoopFsRelationSuite` sometimes (depending on the randomly generated data) will be [failed](https://amplab.cs.berkeley.edu/jenkins/job/SparkPullRequestBuilder/52136/consoleFull) by this bug. After applying this, the test can be passed.

I added a test to `ParquetHadoopFsRelationSuite` with the data which will fail without this patch.

The error exception:

    [info] ParquetHadoopFsRelationSuite:
    [info] - test all data types - StringType (440 milliseconds)
    [info] - test all data types - BinaryType (434 milliseconds)
    [info] - test all data types - BooleanType (406 milliseconds)
    20:59:38.618 ERROR org.apache.spark.executor.Executor: Exception in task 0.0 in stage 2597.0 (TID 67966)
    java.lang.ArrayIndexOutOfBoundsException: 46
	at org.apache.spark.sql.execution.datasources.parquet.VectorizedPlainValuesReader.readBytes(VectorizedPlainValuesReader.java:88)

Author: Liang-Chi Hsieh <viirya@gmail.com>

Closes apache#11418 from viirya/fix-readbytes.

sql/core/src/main/java/org/apache/spark/sql/execution/datasources/parquet/VectorizedPlainValuesReader.java

@@ -85,7 +85,7 @@ public final void readBytes(int total, ColumnVector c, int rowId) {
     for (int i = 0; i < total; i++) {
       // Bytes are stored as a 4-byte little endian int. Just read the first byte.
       // TODO: consider pushing this in ColumnVector by adding a readBytes with a stride.
-      c.putByte(rowId + i, buffer[offset]);
+      c.putByte(rowId + i, Platform.getByte(buffer, offset));
       offset += 4;
     }
   }

sql/hive/src/test/scala/org/apache/spark/sql/sources/ParquetHadoopFsRelationSuite.scala

@@ -175,4 +175,37 @@ class ParquetHadoopFsRelationSuite extends HadoopFsRelationTest {
       }
     }
   }
+
+  test(s"SPARK-13537: Fix readBytes in VectorizedPlainValuesReader") {
+    withTempPath { file =>
+      val path = file.getCanonicalPath
+
+      val schema = new StructType()
+        .add("index", IntegerType, nullable = false)
+        .add("col", ByteType, nullable = true)
+
+      val data = Seq(Row(1, -33.toByte), Row(2, 0.toByte), Row(3, -55.toByte), Row(4, 56.toByte),
+        Row(5, 127.toByte), Row(6, -44.toByte), Row(7, 23.toByte), Row(8, -95.toByte),
+        Row(9, 127.toByte), Row(10, 13.toByte))
+
+      val rdd = sqlContext.sparkContext.parallelize(data)
+      val df = sqlContext.createDataFrame(rdd, schema).orderBy("index").coalesce(1)
+
+      df.write
+        .mode("overwrite")
+        .format(dataSourceName)
+        .option("dataSchema", df.schema.json)
+        .save(path)
+
+      val loadedDF = sqlContext
+        .read
+        .format(dataSourceName)
+        .option("dataSchema", df.schema.json)
+        .schema(df.schema)
+        .load(path)
+        .orderBy("index")
+
+      checkAnswer(loadedDF, df)
+    }
+  }
 }