Fix for SPARK-27259

For compressed files, the size of split can be set to -1. This was
allowed till Spark 2.1 but regressed starting spark 2.2.x

This commit removes the validation on length being at least 0.

Author: prasha2

core/src/main/scala/org/apache/spark/rdd/InputFileBlockHolder.scala

@@ -76,7 +76,6 @@ private[spark] object InputFileBlockHolder {
   def set(filePath: String, startOffset: Long, length: Long): Unit = {
     require(filePath != null, "filePath cannot be null")
     require(startOffset >= 0, s"startOffset ($startOffset) cannot be negative")
-    require(length >= 0, s"length ($length) cannot be negative")
     inputBlock.get().set(new FileBlock(UTF8String.fromString(filePath), startOffset, length))
   }