Globalese integration: error 500 thrown, if no engines are available

To reproduce:

Select a language combination, for which no engine exists in Globalese and start an import until the Globalese integration step occurs.

Now an error 500 is thrown in PHP. 

Instead the user in the front end should see a message:

"No engine exists in Globalese for the current language combination. Please skip the Globalese step of the import".

"Für die aktuelle Sprachkombination existiert keine Engine in Globalese. Bitte überspringen Sie den Globalese Schritt für diesen Import."