[Crash]: Textbuf caret movements with non-trivial scripts (CJK, etc) can trigger NOT_REACHED

[JGRennison]

Version of OpenTTD

master (Linux)

Steps to reproduce

1. Change the font configuration and/or language so that you can insert CJK text
2. Paste some CJK text into a sign or other textbuf
3. Press the left arrow key
4. Press another key to insert a character

Upload crash files

#0  __pthread_kill_implementation (no_tid=0, signo=6, threadid=140737275484928) at ./nptl/pthread_kill.c:44
#1  __pthread_kill_internal (signo=6, threadid=140737275484928) at ./nptl/pthread_kill.c:78
#2  __GI___pthread_kill (threadid=140737275484928, signo=signo@entry=6) at ./nptl/pthread_kill.c:89
#3  0x00007ffff6f9b476 in __GI_raise (sig=sig@entry=6) at ../sysdeps/posix/raise.c:26
#4  0x00007ffff6f817f3 in __GI_abort () at ./stdlib/abort.c:79
#5  0x0000555555ede259 in FatalErrorI(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&) (str="NOT_REACHED triggered at line 267 of /home/jgr/openttd/trunk/src/gfx_layout.cpp")
    at /home/jgr/openttd/trunk/src/openttd.cpp:141
#6  0x0000555555d58cfd in NotReachedError(int, char const*) (line=line@entry=267, file=file@entry=0x555556132650 "/home/jgr/openttd/trunk/src/gfx_layout.cpp") at /home/jgr/openttd/trunk/src/error.cpp:15
#7  0x0000555555d9132a in Layouter::GetCharPosition(char const*) const (this=this@entry=0x7fffffffd1a0, ch=ch@entry=0x555559d0eb24 "은") at /home/jgr/openttd/trunk/src/gfx_layout.cpp:267
#8  0x0000555555d8b3c1 in GetCharPosInString(std::basic_string_view<char, std::char_traits<char> >, char const*, FontSize)Python Exception <class 'gdb.error'>: value has been optimised out
 (str=, ch=ch@entry=0x555559d0eb24 "은", start_fontsize=start_fontsize@entry=FS_NORMAL)
    at /home/jgr/openttd/trunk/src/gfx.cpp:887
#9  0x0000555555ffea98 in Textbuf::UpdateCaretPosition() (this=0x5555596d25c8) at /home/jgr/openttd/trunk/src/textbuf.cpp:295
#10 Textbuf::InsertString(char const*, bool, char const*, char const*, char const*)
    (this=0x5555596d25c8, str=0x7fffffffd2cc "a", marked=marked@entry=false, caret=0x0, insert_location=insert_location@entry=0x0, replacement_end=replacement_end@entry=0x0) at /home/jgr/openttd/trunk/src/textbuf.cpp:210
#11 0x00005555560aa163 in Window::InsertTextString(int, char const*, bool, char const*, char const*, char const*)
    (this=0x5555596d2480, wid=2, str=<optimised out>, marked=<optimised out>, caret=<optimised out>, insert_location=0x0, replacement_end=0x0) at /home/jgr/openttd/trunk/src/window.cpp:2714
#12 0x00005555560ace5d in HandleTextInput(char const*, bool, char const*, char const*, char const*)
    (str=str@entry=0x7fffffffd2cc "a", marked=marked@entry=false, caret=caret@entry=0x0, insert_location=insert_location@entry=0x0, replacement_end=replacement_end@entry=0x0) at /home/jgr/openttd/trunk/src/window.cpp:2730
#13 0x0000555555c7bdcc in VideoDriver_SDL_Base::PollEvent() (this=<optimised out>) at /home/jgr/openttd/trunk/src/video/sdl2_v.cpp:477
#14 0x0000555555c858e5 in VideoDriver::Tick() (this=this@entry=0x555557b3a020) at /home/jgr/openttd/trunk/src/video/video_driver.cpp:135
#15 0x0000555555c7978e in VideoDriver_SDL_Base::LoopOnce() (this=0x555557b3a020) at /home/jgr/openttd/trunk/src/video/sdl2_v.cpp:621
#16 VideoDriver_SDL_Base::LoopOnce() (this=0x555557b3a020) at /home/jgr/openttd/trunk/src/video/sdl2_v.cpp:600
#17 VideoDriver_SDL_Base::MainLoop() (this=0x555557b3a020) at /home/jgr/openttd/trunk/src/video/sdl2_v.cpp:639
#18 0x0000555555ee5afa in openttd_main(int, char**) (argc=<optimised out>, argv=<optimised out>) at /home/jgr/openttd/trunk/src/openttd.cpp:786
#19 0x00007ffff6f82d90 in __libc_start_call_main (main=main@entry=0x5555557befe0 <main(int, char**)>, argc=argc@entry=2, argv=argv@entry=0x7fffffffdba8) at ../sysdeps/nptl/libc_start_call_main.h:58
#20 0x00007ffff6f82e40 in __libc_start_main_impl (main=0x5555557befe0 <main(int, char**)>, argc=2, argv=0x7fffffffdba8, init=<optimised out>, fini=<optimised out>, rtld_fini=<optimised out>, stack_end=0x7fffffffdb98)
    at ../csu/libc-start.c:392
#21 0x0000555555861865 in _start ()

[JGRennison]

It seems that in the ICU implementation ICUVisualRun::GetGlyphToCharMap always starts from 0, instead of being relative to the overall string

[JGRennison]

It seems that the bug is introduced by aed36a6.
Reverting that fixes the problem, but that commit claims to fix something else?