QErrorMessage: put local types into the unnamed namespace

Change-Id: I20f8ea7dc95fdecc4bb1190fb8acda19d99cc234
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@theqtcompany.com>

src/widgets/dialogs/qerrormessage.cpp

@@ -78,6 +78,7 @@ public:
     void retranslateStrings();
 };
 
+namespace {
 class QErrorMessageTextView : public QTextEdit
 {
 public:
@@ -87,6 +88,7 @@ public:
     virtual QSize minimumSizeHint() const Q_DECL_OVERRIDE;
     virtual QSize sizeHint() const Q_DECL_OVERRIDE;
 };
+} // unnamed namespace
 
 QSize QErrorMessageTextView::minimumSizeHint() const
 {