Fix JS errors when Product is not found

[dhardtke]

Description

1. When the galleryRoot element is not present in the DOM, the corresponding component attempts to use an empty object for constructing the list of gallery items. Unfortunately, this object is passed to JSON.parse() which does not accept objects and the code crashes with a SyntaxError.
2. When the SKU element is not present, accessing its innerHTML fails

1. Instead of parsing an object when the galleryRoot is unpresent, the code now simply avoids parsing completely and instead constructs an object to be used as fallback directly.
2. Before accessing the SKU element's innerHTML it is checked that the element exists

Related Issue

Fixes #281.
Fixes #369.

Motivation and Context

How Has This Been Tested?

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have signed the Adobe Open Source CLA.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes and the overall coverage did not decrease.
• All unit tests pass on CircleCi.
• I ran all tests locally and they pass.

[herzog31]

lgtm 👍

Could you please add a test case each for your fixes? You can find related test cases in https://github.com/adobe/aem-core-cif-components/tree/master/ui.apps/test/components/commerce/product.

[dhardtke]

lgtm +1

Could you please add a test case each for your fixes? You can find related test cases in https://github.com/adobe/aem-core-cif-components/tree/master/ui.apps/test/components/commerce/product.

I added a test for the change in product.js but I'm not sure on how to test the change in the Gallery instantiation: The function there is never called in the tests. We'd probably have to move the onDocumentReady function out of the IIFE and call it manually to test it doesn't throw.

[herzog31]

@dhardtke Thanks for your contribution 👍