fix(editor): guard the places where the editor could crash outright

Found with an address and undefined behaviour sanitizer build, random
monkey sessions on the test sceneries and broken inputs:

- A deleted model left its pointer in the pick list of the renderer, the
  bound node of the panels, the bindings of the infrastructure and the
  selection: the next pick or panel frame read freed memory. The renderer
  forgets it, and one erase_model does the cleaning for all the places
  which deleted a model by hand.
- The plan band of a route read the vertex before the first one in the
  frame a drag was let go.
- A scenery which can't be opened goes back to the launcher with the
  reason in the log, a track of an unknown type or a tributary loads as
  a normal track or a river with a message, and a spline with no finite
  length or step gets a sane number of segments.
- Typed numbers which aren't (NaN, inf, ends 0 m or 1000 km apart, a
  vector of 1e30, a diverging track part of 5 km, a curve threshold of 0,
  a zero history size, radius norms below zero) are refused or clamped,
  where they made the geometry run away or divide by zero.
- Folders which can't be read and file names which aren't valid in the
  locale no longer throw out of the scans of sceneries, textures, sweeps,
  roads and signal plates; the scans skip them.
- The launcher: Ctrl+Del with no trainset selected, a dropped vehicle
  whose skin is gone and a text with a percent sign.
- A terrain mesh made for another resolution of its chunk isn't put into
  the chunk, and a slot is reused only for a mesh of the same size.
- Vehicles on a track changed by the editor are moved over a copy of the
  list they leave.
- The table of the keyboard shortcuts gives its stretched column a
  weight, else ImGui divides 0 by 0 in the first frame of the window.

rendering/opengl33renderer.cpp

@@ -5638,6 +5638,13 @@ void opengl33_renderer::Pick_Node_Callback(std::function<void(scene::basic_node
 	m_node_pick_requests.push_back(callback);
 }
 
+void opengl33_renderer::Forget_Node(scene::basic_node const *Node)
+{
+	if (m_picksceneryitem == Node)
+		m_picksceneryitem = nullptr;
+	std::replace_if(m_picksceneryitems.begin(), m_picksceneryitems.end(), [Node](scene::basic_node const *Item) { return Item == Node; }, nullptr);
+}
+
 glm::dvec3 opengl33_renderer::Update_Mouse_Position()
 {
 	if (!m_depth_pointer_pbo->is_busy())