Non-ASCII character may provoke shifted error highlighting

## Information

**VIM version**

VIM - Vi IMproved 8.0 (2016 Sep 12, compiled Mar 18 2020 18:29:15)
Inklusive der Patches: 1-1453

VIM - Vi IMproved 8.2 (2019 Dec 12 kompiliert am Mar 30 2020 22:53:24)
Inklusive der Patches: 1-486

Operating Systems:
- Cygwin on Windows 7 (32 bit): **Vim 8.2**
- Lubuntu 18.04 (32 bit): **Vim 8.0**

## What went wrong

If I use for instance the LanguageTool 'linter' on a plain-text file
```
This is a test..
```
then the double trailing dot is correctly highlighted as error location. As soon as I replace 'a' with 'ä', the hightlighting of '..' shifts by one position to the left. This marking of 't.' is not corrected with the next linter run, and *immeditiately* goes right if I replace the 'ä' with command 'r a'.

Perhaps, the non-ASCII character 'ä' breaks the one-to-one relation between character and byte offsets? As can be seen in the ALEInfo below, LanguageTool correctly reports the error location both for 'a' and 'ä'.

This problem appears whenever a non-ASCII character is present on the same text line at a place before the error highlighting. It disturbs in languages that commonly use such characters, in my case German.

Many thanks for this otherwise fantastic framework!

### :ALEInfo

```
Current Filetype: text
Available Linters: ['alex', 'languagetool', 'proselint', 'redpen', 'textlint',
'vale', 'writegood']
Linter Aliases:
'writegood' -> ['write-good']
Enabled Linters: ['languagetool']
Suggested Fixers:
'remove_trailing_lines' - Remove all blank lines at the end of a file.
'textlint' - Fix text files with textlint --fix
'trim_whitespace' - Remove all trailing whitespace characters at the end of e
very line.
Linter Variables:
Global Variables:
let g:ale_cache_executable_check_failures = v:null
let g:ale_change_sign_column_color = 0
let g:ale_command_wrapper = ''
let g:ale_completion_delay = v:null
let g:ale_completion_enabled = 0
let g:ale_completion_max_suggestions = v:null
let g:ale_echo_cursor = 1
let g:ale_echo_msg_error_str = 'Error'
let g:ale_echo_msg_format = '%code: %%s'
let g:ale_echo_msg_info_str = 'Info'
let g:ale_echo_msg_warning_str = 'Warning'
let g:ale_enabled = 1
let g:ale_fix_on_save = 0
let g:ale_fixers = {}
let g:ale_history_enabled = 1
let g:ale_history_log_output = 1
let g:ale_keep_list_window_open = 0
let g:ale_lint_delay = 200
let g:ale_lint_on_enter = 1
let g:ale_lint_on_filetype_changed = 1
let g:ale_lint_on_insert_leave = 1
let g:ale_lint_on_save = 1
let g:ale_lint_on_text_changed = 'normal'
let g:ale_linter_aliases = {}
let g:ale_linters = {'text': ['languagetool']}
let g:ale_linters_explicit = 0
let g:ale_list_vertical = 0
let g:ale_list_window_size = 10
let g:ale_loclist_msg_format = '%code: %%s'
let g:ale_lsp_root = {}
let g:ale_max_buffer_history_size = 20
let g:ale_max_signs = -1
let g:ale_maximum_file_size = v:null
let g:ale_open_list = 0
let g:ale_pattern_options = v:null
let g:ale_pattern_options_enabled = v:null
let g:ale_set_balloons = 0
let g:ale_set_highlights = 1
let g:ale_set_loclist = 1
let g:ale_set_quickfix = 0
let g:ale_set_signs = 1
let g:ale_sign_column_always = 0
let g:ale_sign_error = '>>'
let g:ale_sign_info = '--'
let g:ale_sign_offset = 1000000
let g:ale_sign_style_error = '>>'
let g:ale_sign_style_warning = '--'
let g:ale_sign_warning = '--'
let g:ale_sign_highlight_linenrs = 0
let g:ale_statusline_format = v:null
let g:ale_sign_style_warning = '--'
let g:ale_sign_warning = '--'
let g:ale_sign_highlight_linenrs = 0
let g:ale_statusline_format = v:null
let g:ale_type_map = {}
let g:ale_use_global_executables = v:null
let g:ale_virtualtext_cursor = 0
let g:ale_warn_about_trailing_blank_lines = 1
let g:ale_warn_about_trailing_whitespace = 1
Command History:
(executable check - success) languagetool
(finished - exit code 0) ['/bin/bash', '-c', '''languagetool'' --autoDetect ''/
home/matthias/z.txt''']
<<>>
20:34:18.463 [main] DEBUG com.optimaize.langdetect.LanguageDetectorImpl - ==> [
DetectedLanguage[en:0.99999461651071]]
1.) Line 1, column 15, Rule ID: DOUBLE_PUNCTUATION
Message: Two consecutive dots
Suggestion: .
This is a test..
^^
Time: 5253ms for 1 sentences (0.2 sentences/sec)
<<>>
(finished - exit code 0) ['/bin/bash', '-c', '''languagetool'' --autoDetect ''/
home/matthias/z.txt''']
<<>>
20:35:03.927 [main] DEBUG com.optimaize.langdetect.LanguageDetectorImpl - ==> [
DetectedLanguage[en:0.9999606576754977]]
1.) Line 1, column 15, Rule ID: DOUBLE_PUNCTUATION
Message: Two consecutive dots
Suggestion: .
This is ä test..
^^
Time: 5067ms for 1 sentences (0.2 sentences/sec)
<<>>
```