If preview generation fails for a file there is no fallback mimetype icon

[nickvergessen]

The activity app is not very forgiving to thumbnail errors. It basically only checks if the mimetype is supported and not whether the actual preview could be generated.

activity/js/script.js

Lines 254 to 257 in cf196a2

	var preview = activity.previews[i];
	content += ((preview.link) ? '<a href="' + preview.link + '">' + "\n" : '')
	+ '<img class="preview' + ((preview.isMimeTypeIcon) ? ' preview-mimetype-icon' : '') + '" src="' + preview.source + '" alt="' + t('activity', 'Open {filename}', preview) + '" />' + "\n"
	+ ((preview.link) ? '</a>' + "\n" : '')

activity/lib/Controller/APIv2Controller.php

Lines 378 to 386 in 8481eb8

	} elseif ($this->preview->isAvailable($fileInfo)) {
	$preview['source'] = $this->urlGenerator->linkToRouteAbsolute('core.Preview.getPreview', [
	'file' => $info['path'],
	'c' => $this->view->getETag($info['path']),
	'x' => 150,
	'y' => 150,
	]);
	$preview['mimeType'] = $fileInfo->getMimetype() ?: 'application/octet-stream';
	$preview['isMimeTypeIcon'] = false;

I guess it should do something like:
https://github.com/nextcloud/spreed/blob/2463190ded52085a0f317dc5b057253aadaa5be4/src/components/MessagesList/MessagesGroup/Message/MessagePart/FilePreview.vue#L404-L412

_Originally posted by @nickvergessen in nextcloud/server#36304

[4y55]

Any solution?