jira: api: Return empty slice instead of panic
jira: api: Return empty slice instead of panic

listStoriesById returns an empty slice now when the list of IDs to fetch is
empty. The function used to panic, but there is actually no reason for this
behaviour really.

Story-Id: SF-114
Change-Id: 5c51c248ea

salsaflow/salsaflow,salsaflow/salsaflow