console.lua: assume non-ASCII characters span 2 cells for truncation

This prevents line wraps in select mode with terminal output which hide
the top items (OSD output no longer uses truncate_utf8 since the
previous commit). This is not ideal as even accented letters are assumed
to be 2 cells wide. The alternative is using \e[?7l and \e[?7h to
disable and enable text wrapping, but it won't work in Windows console
with VT processing disabled.

player/lua/console.lua

@@ -154,8 +154,16 @@ local function truncate_utf8(str, max_length)
     local len = 0
     local pos = 1
     while pos <= #str do
+        local last_pos = pos
         pos = next_utf8(str, pos)
         len = len + 1
+        if pos > last_pos + 1 then
+            if len == max_length - 1 then
+                pos = prev_utf8(str, pos)
+            else
+                len = len + 1
+            end
+        end
         if len == max_length - 1 then
             return str:sub(1, pos - 1) .. '⋯'
         end