Fix: Setting tree lines drawn incorrectly for RTL languages.

[PeterN]

Motivation / Problem

Setting tree lines are drawn incorrectly for RTL languages. At best case the lines are not drawn, at worst case the game can crash in a blitter.

(The blue labels is something else that needs fixing separately)

Description

Fixed by:

1. casting both sides of circle_size ternary result to int to prevent unintended promotion of the just-cast int to unsigned int.
2. Taking account of RTL when applying hsep_normal offset.

Limitations

Checklist for review

Some things are not automated, and forgotten often. This list is a reminder for the reviewers.

• The bug fix is important enough to be backported? (label: 'backport requested')
• This PR touches english.txt or translations? Check the guidelines
• This PR affects the save game format? (label 'savegame upgrade')
• This PR affects the GS/AI API? (label 'needs review: Script API')
  • ai_changelog.hpp, gs_changelog.hpp need updating.
  • The compatibility wrappers (compat_*.nut) need updating.
• This PR affects the NewGRF API? (label 'needs review: NewGRF')
  • newgrf_debug_data.h may need updating.
  • PR must be added to API tracker