v2.12.5 Zim format parser breaks on links with $NAMES with java.lang.IllegalArgumentException

Nobody has claimed this yet.

### ⚠️ This issue respects the following points: ⚠️

- [X] This is a **bug**. Not a [question or feature request](https://github.com/gsantner/markor/issues/new/choose).
- [X] The topic is **not** already reported at [Issues](https://github.com/gsantner/markor/issues?q=#js-issues-search). _(I've searched it)_.
- [X] Markor **is** up to date. See [Releases](https://github.com/gsantner/markor/tags) for the latest version. Updates are available from [F-Droid](https://f-droid.org/en/packages/net.gsantner.markor/) and GitHub.
- [X] The bug is still present in the latest development version (git master). (Please [download](https://nightly.link/gsantner/markor/workflows/build-android-project/master) and try the test version of Markor, named **Marder**. Don't worry; Markor and Marder appear as completely separate applications. You can install both side-by-side, and Markor settings are not touched. In case the issue is resolved there, you don't need to create a bug report. The change will be part of the next Markor update.)

### Description

Trying to view such file:

```
Content-Type: text/x-zim-wiki
Wiki-Format: zim 0.6
Creation-Date: 2000-12-05T16:35:28+03:00

[[https://github.com/b3nj5m1n/xdg-ninja|b3nj5m1n/xdg-ninja: A shell script which checks your $HOME for unwanted files and directories.]]
```

Gives an error:
> Please report at project issue tracker: java.lang.IllegalArgumentException: Illegal group reference

### Steps to reproduce

1. Create zim file
2. Put a link in it with $FOOBAR in title. E.g.: `[[https://google.com|This is $FOOBAR]]`
3. View file via Markor

### Information

Android version: Irrelevant
Device: Irrelevant
App Version: v2.12.5

### Source

F-Droid

### Format / File type

Wikitext, Zim

### Additional info / Log

```shell
-
```

Reproduce the crash by opening a Zim file containing a link title with a value such as $FOOBAR, then trace the Zim/Wikitext parsing path used by Markor. Done means the file opens without IllegalArgumentException and the link title is displayed correctly; add a regression test if the parser's test location is found.

Written by the indexing model from the issue text.