[Bug] Missing picture of dog/cat during the quiz

[Nefariusek]

Description
Sometimes there is no image of an animal. Users can only shoot in the dark. Error in the console appears.

Steps to reproduce

1. Click 'Start Quiz'.
2. Fill the form with settings (20 questions) and click 'START QUIZ'.
3. Navigate around the quiz.
   Note that sometimes a picture is missing and a 404 error is shown.

Desired functionality
Image of animal is always shown.

Screenshots

Additional informations
Error is caused by undefined imageUrl. Filter out such questions after retrieval.