fixed ArrayIndexOutOfBoundsException

git-svn-id: https://hudson.dev.java.net/svn/hudson/trunk/hudson/main@30421 71c3de6d-444a-0410-be80-ed276b4c234a

core/src/main/java/hudson/util/UnbufferedBase64InputStream.java

@@ -39,6 +39,7 @@ public class UnbufferedBase64InputStream extends FilterInputStream {
         if (pos==decoded.length) {
             din.readFully(encoded);
             decoded = Base64.decodeBase64(encoded);
+            if (decoded.length==0)  return -1; // EOF
             pos = 0;
         }