Reproducible urls:
```
https://de.wikipedia.org/w/index.php?title=Datei:Juan_de_Flandes_001.jpg&filetimestamp=00000000000000
https://de.wikipedia.org/w/index.php?title=Datei:Label_for_dangerous_goods_-_class_4.2.svg&filetimestamp=2007081805593
https://de.wikipedia.org/w/index.php?title=File:Not-known.svg&filetimestamp=2007081805593
```
Example trace from Logstash:
```lines=10,counterexample
#0 /srv/mediawiki/php-1.31.0-wmf.21/includes/libs/rdbms/database/Database.php(3184): Wikimedia\Timestamp\ConvertibleTimestamp->getTimestamp(integer)
#1 /srv/mediawiki/php-1.31.0-wmf.21/includes/filerepo/file/OldLocalFile.php(238): Wikimedia\Rdbms\Database->timestamp(string)
#2 /srv/mediawiki/php-1.31.0-wmf.21/includes/filerepo/file/LocalFile.php(311): OldLocalFile->loadFromDB(integer)
#3 /srv/mediawiki/php-1.31.0-wmf.21/includes/filerepo/file/LocalFile.php(628): LocalFile->loadFromCache()
#4 /srv/mediawiki/php-1.31.0-wmf.21/includes/filerepo/FileRepo.php(450): LocalFile->load(integer)
#5 /srv/mediawiki/php-1.31.0-wmf.21/includes/filerepo/RepoGroup.php(154): FileRepo->findFile(Title, array)
#6 /srv/mediawiki/php-1.31.0-wmf.21/includes/GlobalFunctions.php(2928): RepoGroup->findFile(Title, array)
#7 /srv/mediawiki/php-1.31.0-wmf.21/extensions/FlaggedRevs/frontend/FlaggablePageView.php(927): wfFindFile(Title, array)
#8 /srv/mediawiki/php-1.31.0-wmf.21/extensions/FlaggedRevs/frontend/FlaggedRevsUI.hooks.php(162): FlaggablePageView->imagePageFindFile(boolean, boolean)
#9 /srv/mediawiki/php-1.31.0-wmf.21/includes/Hooks.php(177): FlaggedRevsUIHooks::onImagePageFindFile(ImagePage, boolean, boolean)
#10 /srv/mediawiki/php-1.31.0-wmf.21/includes/Hooks.php(205): Hooks::callHook(string, array, array, NULL)
#11 /srv/mediawiki/php-1.31.0-wmf.21/includes/page/ImagePage.php(75): Hooks::run(string, array)
#12 /srv/mediawiki/php-1.31.0-wmf.21/includes/page/ImagePage.php(114): ImagePage->loadFile()
#13 /srv/mediawiki/php-1.31.0-wmf.21/includes/actions/ViewAction.php(68): ImagePage->view()
#14 /srv/mediawiki/php-1.31.0-wmf.21/includes/MediaWiki.php(500): ViewAction->show()
#15 /srv/mediawiki/php-1.31.0-wmf.21/includes/MediaWiki.php(294): MediaWiki->performAction(ImagePage, Title)
#16 /srv/mediawiki/php-1.31.0-wmf.21/includes/MediaWiki.php(861): MediaWiki->performRequest()
#17 /srv/mediawiki/php-1.31.0-wmf.21/includes/MediaWiki.php(524): MediaWiki->main()
#18 /srv/mediawiki/php-1.31.0-wmf.21/index.php(42): MediaWiki->run()
#19 /srv/mediawiki/w/index.php(3): include(string)
#20 {main}
```
I see two problems here:
1. The url parameter should not be unconditionally trusted as if it was a valid timestamp.
2. It seems in this particular case, there is no file by this name. Which means we should probably fail for "unknown file" before we even consider the timestamp in the first place.
I am able to consistently reproduce this on German Wikipedia, but not on Commons. Which suggests that bug number 2 (looking up filetimestamp before knowing that the file is valid) might be specific to FlaggedRevs or some other dewiki extension.