QmlJsEditor: hide context pane if last document is closed

Task-number: QTCREATORBUG-3702
Reviewed-by: Christian Kamm

src/plugins/qmljseditor/qmljseditor.cpp

@@ -691,6 +691,7 @@ QmlJSTextEditorWidget::QmlJSTextEditorWidget(QWidget *parent) :
 
 QmlJSTextEditorWidget::~QmlJSTextEditorWidget()
 {
+    hideContextPane();
     m_semanticHighlighter->abort();
     m_semanticHighlighter->wait();
 }