Blank texts break axes login in GenericPlot

.. for some reason in earlier version of Qt Charts there are errant
   items in the same area as the axes that are blank, these break
   the code that derives the axes rectangles in Qt Charts <= 5.10

src/Charts/GenericPlot.cpp

@@ -271,6 +271,9 @@ GenericPlot::plotAreaChanged()
         foreach(QGraphicsItem *item, qchart->scene()->items(zone, Qt::ItemSelectionMode::ContainsItemShape)) {
             if (item->type() != QGraphicsTextItem::Type) continue;
 
+            // for some reason 5.10 or earlier has errant text items we should ignore
+            if (static_cast<QGraphicsTextItem*>(item)->toPlainText() == "") continue;
+
             // is this an axis title?
             QAbstractAxis *found=NULL;
             foreach(QAbstractAxis *axis, qchart->axes()) {