fix highligh position with unicode characters for neovim

Author: Kamilcuk

autoload/lsp_cxx_hl/textprop_nvim.vim

@@ -19,8 +19,19 @@ function! s:buf_add_hl(buf, ns_id, hl_group,
     " single line symbol
     if a:s_line == a:e_line
         if a:e_char - a:s_char > 0
-            call nvim_buf_add_highlight(a:buf, a:ns_id, a:hl_group,
-                        \ a:s_line, a:s_char, a:e_char)
+            try
+                " Convert byte positions to column position in the file.
+                let line = getbufline(a:buf, a:s_line + 1)[0]
+                call nvim_buf_add_highlight(a:buf, a:ns_id, a:hl_group,
+                            \ a:s_line,
+                            \ byteidx(line, a:s_char),
+                            \ byteidx(line, a:e_char))
+            " If the user fastly edits the file, this can be slower then the
+            " edits, and `getbufline` can return zero lines or these columns
+            " may just not exists anymore.
+            catch /Column value outside range/
+            catch /^Vim\%((\a\+)\)\=:E684/
+            endtry
             return
         else
             return