get rid of an assertion

It's easy for cursor to go off viewport, and that seems fine. Just don't
let a cursor off screen receive keys.

0013-on.keychord_press

@@ -5,7 +5,8 @@ on.keychord_press = function(chord, key)
 		update_font_settings(Current_pane.editor_state.font_height-2)
 	elseif chord == 'C-0' then
 		update_font_settings(20)
-	else
+	elseif Current_pane.editor_state.cursor_x then
+		-- send keys to editor if cursor is visible
 		edit.keychord_press(Current_pane.editor_state, chord, key)
 	end
 end

0014-on.text_input

@@ -1,3 +1,5 @@
 on.text_input = function(t)
+	if Current_pane.editor_state.cursor_x then
 		edit.text_input(Current_pane.editor_state, t)
 	end
+end

0015-on.key_release

@@ -1,3 +1,5 @@
 on.key_release = function(key, scancode)
+	if Current_pane.editor_state.cursor_x then
 		edit.key_release(Current_pane.editor_state, key, scancode)
 	end
+end

edit.lua

@@ -109,7 +109,6 @@ end
 -- return y drawn until
 function edit.draw(State, fg, hide_cursor, show_line_numbers)
   assert(#State.lines == #State.line_cache, ('line_cache is out of date; %d elements when it should be %d'):format(#State.line_cache, #State.lines))
-  assert(Text.le1(State.screen_top1, State.cursor1), ('screen_top (line=%d,pos=%d) is below cursor (line=%d,pos=%d)'):format(State.screen_top1.line, State.screen_top1.pos, State.cursor1.line, State.cursor1.pos))
   State.cursor_x = nil
   State.cursor_y = nil
   local y = State.top