correct bugfix for mouse wheel

Sequence of events in previous scenario:
1. car.draw throws an error
2. The wrapping call_protected invokes send_errors_to_output
3. send_errors_to_output uses Text.insert_text, which was extracted from
   the paste implementation on Nov 20. But it doesn't scroll, and so the
   cursor is off screen.
4. Drawing frames never sets cursor_x or cursor_y.
5. Mouse wheel indirectly requires them to be set. Boom.

edit.lua

@@ -259,7 +259,6 @@ function edit.mouse_wheel_move(State, dx,dy)
     end
   elseif dy < 0 then
     State.cursor1 = {line=State.screen_bottom1.line, pos=State.screen_bottom1.pos}
-    State.cursor_x = 0
     for i=1,math.floor(-dy) do
       Text.down(State)
     end
@@ -373,9 +372,6 @@ function edit.keychord_press(State, chord, key, readonly)
     local before = snapshot(State, before_line)
     local clipboard_data = App.get_clipboard()
     Text.insert_text(State, clipboard_data)
-    if Text.cursor_out_of_screen(State) then
-      Text.snap_cursor_to_bottom_of_screen(State, State.left, State.right)
-    end
     schedule_save(State)
     record_undo_event(State, {before=before, after=snapshot(State, before_line, State.cursor1.line)})
   -- dispatch to text
@@ -394,6 +390,9 @@ function Text.insert_text(State, d)
       Text.insert_at_cursor(State, c)
     end
   end
+  if Text.cursor_out_of_screen(State) then
+    Text.snap_cursor_to_bottom_of_screen(State, State.left, State.right)
+  end
 end
 
 function edit.clear(State)