Metadata coherence accessModeSufficient

Please provide the following details if possible or relevant:

- [1.0.2] the version of Ace impacted by the issue (as returned by the `ace -v` command).
- [v8.7.0] the version of Node used to run Ace (as returned by the `node -v` command).
- [MacOS 10.3.6] your operating system and version.
- [] if the issue is a bug when running Ace: the error message as produced in the log file (you can enable debug logging with the `--verbose` option).
- [] if the issue is about the HTML report: the browser(s) and version(s) you used.
- [] if possible, let us know if you can share a sample input file to help us reproduce the issue.

Let 's say an EPUB has text and images, only. The author of the EPUB has tagged all images with role="decoration" as they do not bear any meaningfull content.
Then this should be fine:
```
textual
visual
textual

```
Even, Ace should report a violation in that case if there a line with:
`visual,textual`

On the contrary, if there at least one image that is not tagged role="decoration", Ace should report a violation if that line with "accessModeSufficient visual,textual" is missing !