Fix NPE since java.io.File.listFiles(FileFilter) can return null.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/io/trunk@1687886 13f79535-47bb-0310-9956-ffa450edef68

Author: garydgregory

src/main/java/org/apache/commons/io/FileUtils.java

@@ -3141,6 +3141,6 @@ public boolean accept(File aFile) {
                     }
                 }
         );
-        return fileInDir.length > 0;
+        return fileInDir != null && fileInDir.length > 0;
     }
 }