Fix the branch links users of the Subversion frontend get when they enter

a wrong revision and only display this list if there are any branches
available for all SCMs.

src/IDF/templates/idf/source/invalid_revision.html

@@ -5,6 +5,7 @@
 <p>{blocktrans}The branch or revision <b>{$commit}</b> is not valid or does not exist
 in this repository.{/blocktrans}</p>
 
+{if count($branches) > 0}
 <p>{blocktrans}The following list shows all available branches:{/blocktrans}</p>
 <ul>
 {foreach $branches as $branch => $path}
@@ -14,6 +15,7 @@ in this repository.{/blocktrans}</p>
 </li>
 {/foreach}
 </ul>
+{/if}
 
 {if $isOwner or $isMember}
 {aurl 'url', 'IDF_Views_Source::help', array($project.shortname)}