OPTIONS: route CANCEL through Strings so a translation mod can reach it

CANCEL is appended after the `ui.options.rows` hook, deliberately -- that is
what stops a mod from orphaning the exit. But it also means no translation
mod can ever see it: there is no row for one to rewrite, and the hook has
already run by the time it is added.

The result is that a fully translated OPTIONS menu has exactly one English
word left on it, and it is the way out. I hit this with a Spanish catalog
where every row translated and the exit did not.

One call, matching how every other label on this screen is already built.
Nothing changes without a catalog loaded: Strings is an identity function
until a mod supplies one.

Follows the same reasoning as #791.

src/ui/OptionsMenu.lua

@@ -585,8 +585,14 @@ function OptionsMenu:update(dt)
 end
 
 function OptionsMenu:draw()
+  -- Through Strings, like every other label on this menu.  CANCEL is
+  -- appended AFTER the rows hook (see the header), which is what keeps a mod
+  -- from orphaning the exit -- but it also means a translation mod never sees
+  -- this string, and cannot: there is no row for it to rewrite.  So the one
+  -- word a Spanish player could not read on a fully translated OPTIONS menu
+  -- was the way out of it.
   OptionRows.draw(self.game, self.rows, self.index, self.scroll or 0,
-                  "CANCEL", #self.rows + 1)
+                  Strings("CANCEL"), #self.rows + 1)
 end
 
 return OptionsMenu