md5hash should not fail silently

git-svn-id: https://svn.apache.org/repos/asf/poi/trunk@1776828 13f79535-47bb-0310-9956-ffa450edef68

src/ooxml/testcases/org/apache/poi/ss/extractor/TestEmbeddedExtractor.java

@@ -109,7 +109,7 @@ public class TestEmbeddedExtractor {
             return DatatypeConverter.printBase64Binary(hash);
         } catch (NoSuchAlgorithmException e) {
             // doesn't happen
-            return "";
+            throw new RuntimeException(e);
         }
     }
 }