Handle a project-template with no jobs

A project may only have jobs attached to it via a projcet-template,
with no project-local jobs.  Because projects and project-templates
share a parser, we need to account for this case, so default the
job list to the empty list.  If someone creates a job-template with
no jobs, that's harmless.

Change-Id: Ibc6f94f38e9d71273180901005166dc191dcdd00
diff --git a/zuul/configloader.py b/zuul/configloader.py
index bca73e3..ea43ab1 100644
--- a/zuul/configloader.py
+++ b/zuul/configloader.py
@@ -158,7 +158,7 @@
             project_template.pipelines[pipeline.name] = project_pipeline
             project_pipeline.queue_name = conf_pipeline.get('queue')
             project_pipeline.job_tree = ProjectTemplateParser._parseJobTree(
-                layout, conf_pipeline.get('jobs'))
+                layout, conf_pipeline.get('jobs', []))
         return project_template
 
     @staticmethod