Call QPainter::end() prior to QPixmapCache::insert()

Inserting a QPixmap with active painters on it causes it to
do a deep copy of it, which is unnecessary.

Task-number: QTBUG-58653
Change-Id: I49123ffcec2e12a01c87974b7a513d68a11185d4
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/libs/utils/stylehelper.cpp

@@ -455,6 +455,7 @@ void StyleHelper::drawIconWithShadow(const QIcon &icon, const QRect &rect,
 
         // Draw the actual pixmap...
         cachePainter.drawPixmap(QRect(QPoint(radius, radius) + offset, QSize(px.width(), px.height())), px);
+        cachePainter.end();
         cache.setDevicePixelRatio(devicePixelRatio);
         QPixmapCache::insert(pixmapName, cache);
     }

src/plugins/coreplugin/fancyactionbar.cpp

@@ -326,6 +326,7 @@ void FancyToolButton::hoverOverlay(QPainter *painter, const QRect &spanRect)
         p.setPen(QPen(grad, 1.0));
         p.drawLine(borderRect.topLeft(), borderRect.topRight());
         p.drawLine(borderRect.bottomLeft(), borderRect.bottomRight());
+        p.end();
 
         QPixmapCache::insert(cacheKey, overlay);
     }

src/plugins/coreplugin/fancytabwidget.cpp

@@ -273,6 +273,7 @@ static void paintSelectedTabBackground(QPainter *painter, const QRect &spanRect)
         p.drawLine(borderRect.topLeft() + QPointF(0, 0), borderRect.topRight());
         p.drawLine(borderRect.topRight() + QPointF(0, 1), borderRect.bottomRight() - QPointF(0, 1));
         p.drawLine(borderRect.bottomLeft() + QPointF(0, -1), borderRect.bottomRight() - QPointF(0, 1));
+        p.end();
 
         QPixmapCache::insert(cacheKey, selection);
     }