Gui: [skip ci] fix size hint of QuantitySpinBox by setting text margins of 2px

See https://forum.freecadweb.org/viewtopic.php?f=3&t=45344

src/Gui/QuantitySpinBox.cpp

@@ -259,6 +259,8 @@ QuantitySpinBox::QuantitySpinBox(QWidget *parent)
     iconLabel->setStyleSheet(QString::fromLatin1("QLabel { border: none; padding: 0px; padding-top: %2px; width: %1px; height: %1px }").arg(iconHeight).arg(frameWidth/2));
     iconLabel->hide();
     lineEdit()->setStyleSheet(QString::fromLatin1("QLineEdit { padding-right: %1px } ").arg(iconHeight+frameWidth));
+    // When a style sheet is set the text margins must for top/bottom must be set to avoid to squash the widget
+    lineEdit()->setTextMargins(0, 2, 0, 2);
 
     QObject::connect(iconLabel, SIGNAL(clicked()), this, SLOT(openFormulaDialog()));
 }