Catch selected concepts element not part of value filter

[juliangruendner]

If an SQ is sent which does not include selectedConcepts in a value filter if the value filter is not of type "concept" flare should be able to process this and not throw an exception

Example sq:

{
"termCodes": [
{
"code": "718-7",
"system": "http://loinc.org",
"display": "Hämoglobin"
}
],
"valueFilter": {
"type": "quantity-comparator",
"comparator": "gt",
"unit": {
"code": "mg/dL",
"display": "mg/dL"
},
"value": 0.0
}
}

where it brakes in the code:
https://github.com/rwth-imi/flare-query/blob/master/mapping/src/main/java/de/rwth/imi/flare/mapping/expansion/QueryExpander.java#L116