Fixed margin of search in Help mode to be consistent with other panels

The margin on the other panels is being set to 4, while the search panel
used the default margin.

src/plugins/help/searchwidget.cpp

@@ -52,6 +52,7 @@ SearchWidget::SearchWidget(QHelpSearchEngine *engine, QWidget *parent)
     , searchEngine(engine)
 {
     QVBoxLayout *vLayout = new QVBoxLayout(this);
+    vLayout->setMargin(4);
 
     resultWidget = searchEngine->resultWidget();
     QHelpSearchQueryWidget *queryWidget = searchEngine->queryWidget();
@@ -76,7 +77,6 @@ SearchWidget::SearchWidget(QHelpSearchEngine *engine, QWidget *parent)
 
 SearchWidget::~SearchWidget()
 {
-    // nothing todo
 }
 
 void SearchWidget::zoomIn()