SW-9312 - Fix Shopware.form.field.Media if the value is undefined or not set.
Merge pull request #1476 in SW/shopware from bugfix/master/sw-9312-fix-form-field-media to master

* commit 'bbe85cc576922a14fdd5426352a0b350bb8993aa':
  SW-9312 - Fix Shopware.form.field.Media if the value is undefined or not set.