Handle products without the images at cart and checkout

[bandieramonte]

This PR aims to fix issue 203, so that items without media images can now be added to the cart.

[CLAassistant]

All committers have signed the CLA.

[vercel]

@bandieramonte is attempting to deploy a commit to the Saleor Commerce Team on Vercel.

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[matteius]

Not sure why the difference, but I am able to add products with out images to the cart. For example: https://mattscoinage.com/default-channel/en-US/products/test-stripe

[bandieramonte]

Not sure why the difference, but I am able to add products with out images to the cart. For example: https://mattscoinage.com/default-channel/en-US/products/test-stripe

Interesting. In any case, I think this new code adds a safety layer for cases without images - it doesn't hurt.
Update: I did note @matteius that the chrome dev tools show a 400 GET error when adding an item without image to the cart in your link.

[krzysztofwolski]

LGTM 👍

[krzysztofwolski]

Tested locally, and indeed it solves the issue with the products without the images :)
Thanks for your contribution!