After interruption, TTS restarts at wrong place

# Issue details

### Duplicate?
Have you searched the issues of this repository if your issue is already known? yes/no

Yes, I haven't found it. I may have missed it—if so, apologies.

### Actual behaviour

When I'm listening to TTS (my main way of using the app), and there is some kind of interruption (such as a text message ping or a voice instruction from a navigation app), TTS re-starts after the interruption not where it left off but where I initially started it (usually the beginning of the article). This makes the app largely unusable, for instance, while running a navigation app and driving.

### Expected behaviour

TTS playback should continue after the interruption where it left off.

# Steps to reproduce the issue
1. Begin TTS playback
2. Receive instruction from an app like Google Maps or receive a text message
3. TTS re-starts where it first began

# Environment details
- **wallabag app version**: 2.3.0
- **wallabag app installation source** (e.g. Gplay, F-Droid, manual): F-Droid
- **Android OS version**: 9
- **Android ROM** (e.g. stock, LineageOS, SlimRom,…): LineageOS
- **Android hardware**: Moto X
- **wallabag server version**: 2.4.0-dev

# Your experience with wallabag Android app
Have you had any luck using wallabag Android app before? (Sometimes we get tired of reading bug reports all day and a lil' positive end note does wonders)

I love the app and use it daily. It is mostly an excellent experience. Thank you so much for all you do!