QCommonStyle: Add SP_DialogNoButton case in standardIcon

It is present in standardPixmap but missing from standardIcon resulting in
QMessageBox using the fallback PNG provided by Qt for the "No" button.

Change-Id: If4f14c7de26eb32277cd19a7be75360dba4f4e29
Reviewed-by: Christian Ehrlicher <ch.ehrlicher@gmx.de>

src/widgets/styles/qcommonstyle.cpp

@@ -5967,6 +5967,7 @@ QIcon QCommonStyle::standardIcon(StandardPixmap standardIcon, const QStyleOption
         case SP_ArrowLeft:
                 icon = QIcon::fromTheme(QLatin1String("go-previous"));
                 break;
+        case SP_DialogNoButton:
         case SP_DialogCancelButton:
                 icon = QIcon::fromTheme(QLatin1String("dialog-cancel"),
                                         QIcon::fromTheme(QLatin1String("process-stop")));