the content of preview might change its position when tab-browsing in the editor with snippet false

[ralf3u]

Steps to reproduce

• open Geany with two documents: one very long txt-document and one very long html-document
• html-document is in focus
• close Geany
• open Geany (result: the content of preview is on top)
• tab-browse with the mouse or with shortcuts in the editor, and then back to the html-document (result: the content of preview is not any more on top)

Expectation
The content of preview should not change its position during tab-browsing in the editor. It should stay on top.

Remark

• the issue does not occur with a very short txt-document
• the issue appears for fountain, html and md
• the issue is a big problem because it has an impact on issue number 23

Possible solution
When tab-browsing on a document with snippet true, then it does not reset something when tab-browsing on a document with snippet false, and that is why the content is changing its position. Evidence: The issue does not appear when tab-browsing only between fountain-documents and html-documents, both very long, and both with snippet false.

[ralf3u]

If I change in preview.conf snippet_pandoc=true to snippet_pandoc=false (Edit,Preferences Plugin, Preview, Reload Config, Apply and OK), then the issue does not exist any more. But that does not mean that the issue is fixed.

[xiota]

The scroll position for snippets mode will be unstable until I can figure out how to sync the editor and webview.

For the other documents, the scroll position might be saved/restored with the wrong index when the document is switched. I'll have to review the code and see if I can spot the mistake.

[ralf3u]

Remark
Because of issue number 29 is nearly solved, there is now an empty preview for txt-documents, so the issue can not be reproduced with txt-documents at the moment. But the issue can be reproduced with long fountain-documents with snippet_fountain=true.

[ralf3u]

Today, I can not reproduce the issue when snippet of html and md are false, neither with html, nor with md. For fountain, I can't do tests because of xiota/geanylua-scripts#5. But I think that the issue will also not appear there.