Missing pages causes server error

[jochenklar]

As reported by @jmfrenzel , catalogs with sections without pages cause a server error when creating the answer tree. The bug is in rdmo/projects/answers.py, Line 82.

[MyPyDavid]

We also had this error:

Exception Type: 	IndexError
Exception Value: 	list index out of range

Exception Location: 	/srv/rdmo/env/../rdmo/projects/answers.py, line 82, in compute_element_node
Raised during: 	rdmo.projects.viewsets.ProjectViewSet

at:

rdmo/rdmo/projects/answers.py

Line 82 in 8737fb0

element_node['first'] = element_node['elements'][0]['id']

for:

element 	
<Section: https://rdmo.example.de/terms/questions/General>

element_node 	
{'elements': [],
 'id': 123,
 'model': 'questions.section',
 'show': True,
 'title': 'Allgemeine Infos',
 'uri': 'https://rdmo.example.de/terms/questions/General'}

element_type 	
'section'