DecimalType is not read back when non-native type exists

Author: Davies Liu

sql/core/src/main/scala/org/apache/spark/sql/parquet/ParquetConverter.scala

@@ -244,7 +244,7 @@ private[parquet] abstract class CatalystConverter extends GroupConverter {
    * Read a decimal value from a Parquet Binary into "dest". Only supports decimals that fit in
    * a long (i.e. precision <= 18)
    */
-  protected[parquet] def readDecimal(dest: Decimal, value: Binary, ctype: DecimalType): Unit = {
+  protected[parquet] def readDecimal(dest: Decimal, value: Binary, ctype: DecimalType): Decimal = {
     val precision = ctype.precisionInfo.get.precision
     val scale = ctype.precisionInfo.get.scale
     val bytes = value.getBytes