[stable27] fix: handle exif metadata read errors gracefully

[st3iny]

• Resolves: none

Summary

The ExifProvider does not check if the given $file can be read before attempting to extract metadata. I improved the code a bit by only calling getimagesizefromstring if $file->getContent() is not false.

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)