Fix subsetting on string variables with newlines

[dmgaldi]

Overview

Example

OBI_0001622 has newlines in the megastudy which breaks the CSV parser in merging component.

{
    "studyId": "VBP_MEGA",
    "derivedVariables": [],
    "filters": [],
    "entityId": "GAZ_00000448",
    "outputVariables": [
        {
            "entityId": "GAZ_00000448",
            "variableId": "EUPATH_0043203"
        },
        {
            "entityId": "GAZ_00000448",
            "variableId": "OBI_0001620"
        },
        {
            "entityId": "GAZ_00000448",
            "variableId": "OBI_0001621"
        },
        {
            "entityId": "EUPATH_0000605",
            "variableId": "OBI_0001622"
        }
    ]
}