Avoid error log from velocity if no custom e-mail template exists

The code to determine the template that should be used for sending an
e-mail notification first tries to load a custom e-mail template and
only if a custom template cannot be found it falls back to the
default template. The problem is that trying to load a non-existing
custom e-mail template results in an error log, e.g.:
  ERROR velocity : ResourceManager : unable to find resource
    'ChangeSubject.vm' in any resource loader.

The new code checks whether a custom template exists before trying
to load it.

Change-Id: Icec3067792f1d2102a11bec1356844280b9e72f9
Signed-off-by: Edwin Kempin <edwin.kempin@sap.com>

gerrit-server/src/main/java/com/google/gerrit/server/mail/OutgoingEmail.java

@@ -374,13 +374,10 @@ public abstract class OutgoingEmail {
   protected String velocifyFile(String name) throws EmailException {
     try {
       RuntimeInstance runtime = args.velocityRuntime;
-      Template template;
-      try {
-        template = runtime.getTemplate(name, "UTF-8");
-      } catch (org.apache.velocity.exception.ResourceNotFoundException notFound) {
+      if (runtime.getLoaderNameForResource(name) == null) {
         name = "com/google/gerrit/server/mail/" + name;
-        template = runtime.getTemplate(name, "UTF-8");
       }
+      Template template = runtime.getTemplate(name, "UTF-8");
       StringWriter w = new StringWriter();
       template.merge(velocityContext, w);
       return w.toString();