Some characters are invisible with cascadia-code font

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**Describe the bug**

1. Download Cascadia-code font from official repository:
`https://github.com/microsoft/cascadia-code/releases`
2. Install it
3. Set it as font used within guake

**Expected behavior**


**Actual behavior**

**To Reproduce**
Just type inside guake:
```
pwegrzynek@WegrzyNET:~$ echo "4+4=8"
4+4=8
pwegrzynek@WegrzyNET:~$ echo "4+4==8"
4+4==8
pwegrzynek@WegrzyNET:~$ echo "4+4===8"
4+4===8
pwegrzynek@WegrzyNET:~$
```

It seems that whenever Cascadia has the ability to join two or more chars, does not display anything, or display it wrong

For example:


-------------------------------------------------------------------------------

Please run `$ guake --support`, and paste the results here. Don't put backticks (`` ` ``) around it! The output already contains Markdown formatting. And make sure you run the command **OUTSIDE** the Guake.

pwegrzynek@WegrzyNET:~$ guake --support
[WARN] Unable to load the library libutempter !
[WARN] The command will not work in guake !
[WARN] libutempter.so.0: nie można otworzyć pliku obiektu dzielonego: Nie ma takiego pliku ani katalogu
Usage: main.py [options]

main.py: error: no such option: --support