Chapters without images leaves a blank space with broken image
### Describe the bug
If no image is added to a chapter, an blank space is left. The problem is that some browsers, like Chrome, display a broken image.
2 minor bugs also :
- `Chapters` is not translated
- The number of chapters is left blank
### Steps to reproduce
Example : https://podcast.jplus7.fr/@jplus7/episodes/j7-19-02-2024/chapters
### Expected behavior
The episode cover should be the default image, or no image should be displayed if there isn't one.
### Actual behavior
### Relevant logs and/or screenshots
### Context
- Castopod: v 1.10.2
- Browser: Chrome 121.0.6167.185
### Possible fixes
[If you can, link to the line of code that might be responsible for the problem]
issue