Noticed today while building [master](8a56f79d491271120abc3843c46e9dda44edd308).


```bash
GUI: Using QCharRef with an index pointing outside the valid range of a QString. The corresponding behavior is deprecated, and will be changed in a future version of Qt.
```

From a quick look the issue is somewhere in [splashscreen.cpp](https://github.com/bitcoin/bitcoin/blob/master/src/qt/splashscreen.cpp). 

You should see the warning if you quit while the splashscreen is still displayed. Likely requires a recent version of Qt (I'm using 5.14.1).

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pixPaint.drawText(pixmap.width()/devicePixelRatio-titleTextWidth-paddingRight+2,paddingTop+titleVersionVSpace,versionText);
    
    {
        pixPaint.setFont(QFont(font, 10*fontFactor));
        const int x = pixmap.width()/devicePixelRatio-titleTextWidth-paddingRight;
        const int y = paddingTop+titleCopyrightVSpace;
        QRect copyrightRect(x, y, pixmap.width() - x - paddingRight, pixmap.height() - y);
        pixPaint.drawText(copyrightRect, Qt::AlignLeft | Qt::AlignTop | Qt::TextWordWrap, copyrightText);
    }
    
    if(!titleAddText.isEmpty()) {
        QFont boldFont = QFont(font, 10*fontFactor);
        boldFont.setWeight(QFont::Bold);
        pixPaint.setFont(boldFont);
        fm = pixPaint.fontMetrics();
        int titleAddTextWidth  = GUIUtil::TextWidth(fm, titleAddText);
        pixPaint.drawText(pixmap.width()/devicePixelRatio-titleAddTextWidth-10,15,titleAddText);
    }
    pixPaint.end();
    
    setWindowTitle(titleText + " " + titleAddText);
    
    QRect r(QPoint(), QSize(pixmap.size().width()/devicePixelRatio,pixmap.size().height()/devicePixelRatio));
    resize(r.size());
    setFixedSize(r.size());
    move(QGuiApplication::primaryScreen()->geometry().center() - r.center());
    subscribeToCoreSignals();
    installEventFilter(this);
}
SplashScreen::~SplashScreen()