crash fix: double slider can have strange array size...

FIXME: investigate further. m_layers_values.
size can be == 3 + m_values, and get_layer_number return m_values.size() (with wipe tower)
is it normal?

src/slic3r/GUI/DoubleSlider.cpp

@@ -783,9 +783,10 @@ wxString Control::get_label(int tick, LabelType label_type/* = ltHeightWithLayer
  return str;
  if (label_type == ltHeightWithLayer) {
  size_t layer_number = m_is_wipe_tower ? get_layer_number(value, label_type) + 1 : (m_values.empty() ? value : value + 1);
+ layer_number = std::min(m_values.size() - 1, layer_number);
  double layer_height = m_values.empty() ? m_label_koef : m_values[layer_number - 1] - (layer_number > 1 ? m_values[layer_number - 2] : 0);
  return format_wxstr("%1%\n(%2%,\n%3%)", str, wxString::Format("%.*f", 2, layer_height), layer_number);
- }
+  }
  }
 
  return wxEmptyString;