DiffEditor: Silence warning about unused variable.

Change-Id: I18a6dd021bb29ca5eaa7727213c80458d903ee6c
Reviewed-by: Tobias Hunger <tobias.hunger@theqtcompany.com>

src/plugins/diffeditor/diffeditorplugin.cpp

@@ -175,9 +175,8 @@ void DiffEditorPlugin::diff()
     if (!document)
         return;
 
-    DiffEditorController *controller = DiffEditorController::controller(document);
-    if (!controller)
-        controller = new FileDiffController(document, fileName1, fileName2);
+    if (!DiffEditorController::controller(document))
+        new FileDiffController(document, fileName1, fileName2);
     Core::EditorManager::activateEditorForDocument(document);
     document->reload();
 }