Update getfood.php

!!! Previous Fix had some side-effect in JSON-structure, this one works :)
Sometimes, not all found links to the PDFs are valid => wget creates a pdf with 0 byte => no *.xml will be created => xml parser chokes => PHP exits.
This fix checks if there was a xml-file generated.
Merge pull request #2 from Taxilof/patch-2

Update getfood.php - please discard previous pull request