QmlDesigner: Reset ComponentTextModifier when changing to doc model

A dangling ComponentTextModifier would still handle signals, so delete
it when it is no longer needed.

Change-Id: I67a70cf8b5e304a627ef92f9b4b8beecdd63cf0f
Reviewed-by: Thomas Hartmann <thomas.hartmann@qt.io>

src/plugins/qmldesigner/components/integration/designdocument.cpp

@@ -311,6 +311,7 @@ void DesignDocument::changeToDocumentModel()
     viewManager().detachViewsExceptRewriterAndComponetView();
 
     m_inFileComponentModel.reset();
+    m_inFileComponentTextModifier.reset();
 
     viewManager().attachRewriterView();
     viewManager().attachViewsExceptRewriterAndComponetView();