Fix misaligned icons in wxTreeCtrl for wxQt

Center the items vertically, as this looks much better, and is also more
consistent with the appearance in the generic version, which was
previously used.

Closes https://github.com/wxWidgets/wxWidgets/pull/1378

src/qt/treectrl.cpp

@@ -222,7 +222,8 @@ protected:
             const wxImageList *imageList = GetHandler()->GetImageList();
             const wxBitmap bitmap = imageList->GetBitmap(imageIndex);
             const QRect rect = visualRect(index);
-            painter->drawPixmap(rect.topLeft(), *bitmap.GetHandle());
+            const int offset = (rect.height() / 2) - (bitmap.GetHeight() / 2);
+            painter->drawPixmap(rect.topLeft() + QPoint(0,offset), *bitmap.GetHandle());
         }
     }