Fix pointer truncation in wxListEvent::GetData() in LLP64 builds.

We must use wxUIntPtr and not long here to avoid truncating the upper half of
the pointer when sizeof(void*)>sizeof(long).

Closes #15578.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@75005 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/listbase.h

@@ -510,7 +510,7 @@ public:
     const wxString& GetLabel() const { return m_item.m_text; }
     const wxString& GetText() const { return m_item.m_text; }
     int GetImage() const { return m_item.m_image; }
-    long GetData() const { return static_cast<long>(m_item.m_data); }
+    wxUIntPtr GetData() const { return m_item.m_data; }
     long GetMask() const { return m_item.m_mask; }
     const wxListItem& GetItem() const { return m_item; }