(refs #47) At least one file is required

Author: takezoe

src/main/twirl/gitbucket/gist/edit.scala.html

@@ -115,6 +115,10 @@ <h1 style="margin: 0px;">New snippet</h1>
           }
         }
       }
+      if(value == null){
+        displayError('At least one file is required.');
+        return false;
+      }
       return true;
     });