bugfix: up-arrow when cursor straddles a wrapping line

We can have multiple rects corresponding to the same location. But only
one of them has show_cursor enabled. This disambiguates which one we
mean.

With the current rect-based design, it's much harder to get 2 cursors
than I thought.

move.lua

@@ -282,7 +282,7 @@ function edit.to_coord(editor, loc)  -- scans
         -- text
         for _,s in ipairs(rect.screen_line_rects) do
           for _,c in ipairs(s.char_rects) do
-            if c.pos == loc.pos then
+            if c.pos == loc.pos and c.show_cursor then
               return editor.left + c.x, y + c.y
             end
           end