[translatable] query walker fix, closes #88

lib/Gedmo/Translatable/Query/TreeWalker/TranslationWalker.php

@@ -204,7 +204,9 @@ class TranslationWalker extends SqlWalker
     public function walkFromClause($fromClause)
     {
         $result = parent::walkFromClause($fromClause);
-        $result .= $this->translationJoinSql[0];
+        if (count($this->translationJoinSql)) {
+            $result .= $this->translationJoinSql[0];
+        }
         return $result;
     }