check dir existing and return empty List as default.

Author: viirya

core/src/main/scala/org/apache/spark/util/Utils.scala

@@ -659,11 +659,15 @@ private[spark] object Utils extends Logging {
   }
 
   private def listFilesSafely(file: File): Seq[File] = {
-    val files = file.listFiles()
-    if (files == null) {
-      throw new IOException("Failed to list files for dir: " + file)
+    if (file.exists()) {
+      val files = file.listFiles()
+      if (files == null) {
+        throw new IOException("Failed to list files for dir: " + file)
+      }
+      files
+    } else {
+      List()
     }
-    files
   }
 
   /**