Maint.ts crashed when no supporter

I just created a BMAC account and set up the action `Buy Me A Coffee Reade` that leverages this package.

I still haven't received any donations, and the action fails with this error:
```log
Run akosbalasko/coffee-to-file@1.0.1
with:
BUY_ME_A_COFFEE_TOKEN: ***
NUMBER_OF_MESSAGES: 3
FILENAME: README.md
Error: Cannot read properties of undefined (reading 'slice')
```

The cause is that the BMAC api probably returns an array with null or undefined data.
I created a patch for this and would like to contribute!
Since I found no guidelines, I'm starting with opening this issue. PR incoming