[Bug 57809] New: cmd: Incorrect substring expansion of last character (e.g. `!MY_STR:~1!`)

[WineHQ Bugzilla]

https://bugs.winehq.org/show_bug.cgi?id=57809

Bug ID: 57809
           Summary: cmd: Incorrect substring expansion of last character
                    (e.g. `!MY_STR:~1!`)
           Product: Wine
           Version: 10.0
          Hardware: x86-64
                OS: Linux
            Status: UNCONFIRMED
          Severity: major
          Priority: P2
         Component: cmd
          Assignee: [e-mail]
          Reporter: [e-mail]
      Distribution: ---

Call the following script and observe the different output on Windows and Wine.
Substring expansion seems to work in general except the last character,
therefore MY_STR is set to 1 character to trigger the issue immediately.

Note that I've focused on the issue at hand and haven't tried out other
variations of substring-expansion.

issue_substring_expansion.bat
```cmd
@echo off

setlocal enableextensions enabledelayedexpansion

set MY_STR=R
echo "!MY_STR:~1!"
REM Prints "" on Windows
REM Prints "R" on Wine
```

This issue is blocking to get PlanAhead (part of Xilinx ISE 14.7) to work.
Multiple batch scripts set-up the environment before starting the GUI. Because
of this issue, they end up in an endless loop while iterating over all
characters in a variable similar to PATH.

My version:

```console
$ wine --version
wine-10.0 (Staging)
```