Improve per-monitor DPI in wxVListBoxComboPopup

Adjust the default item height before the drawing size is calculated.

include/wx/odcombo.h

@@ -93,6 +93,7 @@ public:
     virtual void OnComboDoubleClick() wxOVERRIDE;
     virtual bool LazyCreate() wxOVERRIDE;
     virtual bool FindItem(const wxString& item, wxString* trueItem) wxOVERRIDE;
+    virtual void OnDPIChanged(wxDPIChangedEvent& event);
 
     // Item management
     void SetSelection( int item );

src/generic/odcombo.cpp

@@ -84,6 +84,10 @@ bool wxVListBoxComboPopup::Create(wxWindow* parent)
     // TODO: Move this to SetFont
     m_itemHeight = m_combo->GetCharHeight();
 
+    // Bind to the DPI event of the combobox. We get our own once the popup
+    // is shown, but this is too late, m_itemHeight is already being used.
+    m_combo->Bind(wxEVT_DPI_CHANGED, &wxVListBoxComboPopup::OnDPIChanged, this);
+
     return true;
 }
 
@@ -104,6 +108,11 @@ void wxVListBoxComboPopup::SetFocus()
 #endif
 }
 
+void wxVListBoxComboPopup::OnDPIChanged(wxDPIChangedEvent& WXUNUSED(event))
+{
+    m_itemHeight = m_combo->GetCharHeight();
+}
+
 bool wxVListBoxComboPopup::LazyCreate()
 {
     // NB: There is a bug with wxVListBox that can be avoided by creating