Bad import of PDF text loses a double 'f'
#### Summary:
Somehow, importing the attached PDF results in a lost letter.
#### Steps to reproduce:
- download this pdf: [plot_NNI_4_skinny.pdf](/uploads/34b394d600bd9bbb6fb9dc9e18d43eda/plot_NNI_4_skinny.pdf)
- import it in inkscape
#### What happened?
([2021-02-27_09-46](/uploads/0b1fd672b597aa40d99c1d8d6ee1b7e6/2021-02-27_09-46.png))
#### What should have happened?
#### Version Info:
```
- Inkscape Version: 0.92.3 all the way till 1.0.2
- Operating System: Ubuntu 18.04 all the way till Debian sid at 2021-02-27
```
Original reported in this [Ubuntu bug #1793881](https://bugs.launchpad.net/ubuntu/+source/inkscape/+bug/1793881)
issue