Add orphan inline images below the message body

[bohwaz]

• In plaintext mode: all inline images will be displayed below the message body
• In HTML mode: all inline images that are not referenced in the message HTML body will be listed below the message body

This doesn't add more CPU usage as it is using the already called HTML filtering function to discover if an inline part is referenced or not.

This fixes issue #5051 and is a bit better than #9150

[bohwaz]

Not sure why CI is failing, but it's not on any code I changed in this PR.

[alecpl]

I think this is wrong because you display the images even if inline_images is false. With this option disabled they should appear on the attachments list, not below the body.

[bohwaz]

I think this is wrong because you display the images even if inline_images is false. With this option disabled they should appear on the attachments list, not below the body.

@alecpl As far as I understand the code of Roundcube, it is not possible to do what you want currently as the message body is parsed after the display of the attachments, so there is no way to know if the message parts are not in the message body.

This is why I'm appending the parts below the message and not in the message list. Please suggest a code fix if I'm wrong as I'm not familiar with the internals of Roundcube.

[pabzm]

@bohwaz The references are actually collected when parsing the message. You can collect them from there, as #9472 does. If that PR gets merged (and doesn't "accidentally" fix the issues you mentioned here), you'll be able to easily implement your idea, I think.

[bohwaz]

I think your PR solves this issue as well, but I have zero time to invest in this currently. I'll check this later maybe.