ui: fixed fontMetrics lineheight working with wrong font in QtCodeSnippet

FontMetric specific settings are now applied in the showEvent method, which is executed right before showing the Widget
where the font setting from the stylesheet is already present.

src/app/qt/element/QtCodeSnippet.h

@@ -55,7 +55,8 @@ public:
 	void annotateText(const TokenLocationFile& locationFile);
 
 protected:
-	void resizeEvent(QResizeEvent *event);
+	virtual void resizeEvent(QResizeEvent *event);
+	virtual void showEvent(QShowEvent* event);
 
 private slots:
 	void updateLineNumberAreaWidth(int newBlockCount);