Examples: changes to static_cast in Qt5 client example

As suggested by @dantti

examples/client/qt5client.cpp

@@ -47,7 +47,7 @@ class VncViewer : public QWidget
 
 void VncViewer::finishedFramebufferUpdateStatic(rfbClient *cl)
 {
-    VncViewer *ptr = (VncViewer *) rfbClientGetClientData(cl, nullptr);
+    VncViewer *ptr = static_cast<VncViewer*>(rfbClientGetClientData(cl, nullptr));
     ptr->finishedFramebufferUpdate(cl);
 }