fix failed assertions in wxqt from newer wx library code

src/qt/choice.cpp

@@ -74,7 +74,7 @@ bool wxChoice::Create( wxWindow *parent, wxWindowID id,
         const wxValidator& validator,
         const wxString& name )
 {
-    return Create( parent, id, pos, size, choices.size(), &choices[ 0 ], style,
+    return Create( parent, id, pos, size, choices.size(), choices.size() ? &choices[ 0 ] : NULL, style,
         validator, name );
 }
 

src/qt/dc.cpp

@@ -24,6 +24,8 @@
 #include "wx/qt/private/converter.h"
 #include "wx/qt/private/utils.h"
 
+#include <QtGui/QScreen>
+#include <QtWidgets/QApplication>
 
 static void SetPenColour( QPainter *qtPainter, QColor col )
 {
@@ -124,7 +126,10 @@ int wxQtDCImpl::GetDepth() const
 
 wxSize wxQtDCImpl::GetPPI() const
 {
-    return wxSize(m_qtPainter->device()->logicalDpiX(), m_qtPainter->device()->logicalDpiY());
+    QScreen *srn = QApplication::screens().at(0);
+    qreal dotsPerInch = (qreal)srn->logicalDotsPerInch();
+    return wxSize(round(dotsPerInch), round(dotsPerInch));
+//    return wxSize(m_qtPainter->device()->logicalDpiX(), m_qtPainter->device()->logicalDpiY());
 }
 
 void wxQtDCImpl::SetFont(const wxFont& font)

src/qt/evtloop.cpp

@@ -115,7 +115,9 @@ int wxQtEventLoopBase::DispatchTimeout(unsigned long timeout)
 
 void wxQtEventLoopBase::WakeUp()
 {
-    QAbstractEventDispatcher::instance()->wakeUp();
+    QAbstractEventDispatcher *instance = QAbstractEventDispatcher::instance();
+    if(instance)
+        instance->wakeUp();
 }
 
 void wxQtEventLoopBase::DoYieldFor(long eventsToProcess)

src/qt/window.cpp

@@ -562,9 +562,8 @@ void wxWindowQt::SetScrollbar( int orientation, int pos, int thumbvisible, int r
 void wxWindowQt::SetScrollPos( int orientation, int pos, bool WXUNUSED( refresh ))
 {
     wxScrollBar *scrollBar = QtGetScrollBar( orientation );
-    wxCHECK_RET( scrollBar, "Invalid scrollbar" );
+    if(scrollBar)
-
+        scrollBar->SetThumbPosition( pos );
-    scrollBar->SetThumbPosition( pos );
 }
 
 int wxWindowQt::GetScrollPos( int orientation ) const