Bug fix on job version testing

This patch suggests two bug fixes. The first one return an empty string
in the case of the user doesn't send any parameters for the application.
The second bug fix is related to the test of an existing commited app version.
The test of the existing version wasn't done before requesting the app
version itself. This patch corrects it.
Signed-off-by: Matthieu Berjon <matthieu.berjon@inria.fr>

django/allgo/api/v1/views.py

@@ -73,12 +73,11 @@ def jobs(request):
             return JsonResponse({'error': 'Unknown queue'}, status=400)
 
     log.info("Job submit by user %s", user)
-    job = Job.objects.create(param=request.POST['job[param]'], queue=queue, webapp=app, user=user.user)
-    job.version = app.get_webapp_version().number  # TODO: add version selection in the api
-    if job.version is None:
+    job = Job.objects.create(param=request.POST.get('job[param]', ''), queue=queue, webapp=app, user=user)
+    if app.get_webapp_version() is None:
         log.debug('No usable versions')
         return JsonResponse({'error': "This app is not yet published"}, status=404)
-
+    job.version = app.get_webapp_version().number  # TODO: add version selection in the api
     upload_data(request.FILES.values(), job)
 
     # run the Job validators