Fix EZP-23420: Log error if source image doesn't exist

> https://jira.ez.no/browse/EZP-23420

Closes #1020 (commit cherry-picked). Now also catches `NotResolvableException` in case the image variation is not present.
Tests have been added too.
Does not belong here, as it is not defined as thrown in any of the interfaces, and alternative implementation might not use it. `eZ/Bundle/EzPublishCoreBundle/Imagine/Exceptions` should be the right place. The same for `InvalidVariationException` though it was not introduced here.