Avoid exception when File is a folder, just skip it.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/codec/trunk@1744343 13f79535-47bb-0310-9956-ffa450edef68

Author: garydgregory

src/main/java/org/apache/commons/codec/digest/Digest.java

@@ -112,7 +112,9 @@ private void run(String prefix, final MessageDigest messageDigest) throws IOExce
 
     private void run(String prefix, MessageDigest messageDigest, File[] files) throws IOException {
         for (File file : files) {
-            println(prefix, DigestUtils.digest(messageDigest, file));
+            if (file.isFile()) {
+                println(prefix, DigestUtils.digest(messageDigest, file));
+            }
         }
     }