Fix crash when changing wxQt wxScrollBar position

wxScrollBar::SetScrollbar() now blocks the signals of QScrollBar before
setting a value, which avoids behaviour where slots are called before
the QScrollBar is displayed.

Closes https://github.com/wxWidgets/wxWidgets/pull/1050

src/qt/scrolbar.cpp

@@ -100,7 +100,9 @@ void wxScrollBar::SetScrollbar(int position, int WXUNUSED(thumbSize),
     {
         m_qtScrollBar->setRange( 0, range - pageSize );
         m_qtScrollBar->setPageStep( pageSize );
+        m_qtScrollBar->blockSignals(true);
         m_qtScrollBar->setValue( position );
+        m_qtScrollBar->blockSignals(false);
         m_qtScrollBar->show();
     }
     else