OSRM table error with single-location instance

[jcoupey]

This is an edge case somehow similar to #291. When solving a single-location instance (same location for vehicle and job) such as:

{
  "vehicles": [
    {
      "id": 1,
      "start": [2.35044, 48.71764]
    }
  ],
  "jobs": [
    {
      "id": 1,
      "location": [2.35044, 48.71764]
    }
  ]
}

then the OSRM table request contains only one location (input locations are deduplicated). Instead of the expected trivial one-step route, we get an error:

{"code":3,"error":"OSRM table: Number of coordinates needs to be at least two."}