Call to a member function getGroupType() on null

Haven't found a way to reproduce this, but in watchdog we sometimes find this exception thrown in Drupal\entitygroupfield\Plugin\Field\FieldWidget\EntityGroupFieldWidgetBase::addMoreSubmit line 865.

Looking at the code, it is generally recommended checking the result of a load operation on storage, so I'm going to provide a safety enhancement in an MR to avoid this exception regardless how it is caused.