Make test base64 data valid (#2973)

* Make user VLR handling robust.

* Cleanup.

* Remove dead header.

* Make things with with Ext VLRs.

* Add more test.

* One more test.

* Remove unnecessary cast.

* Add a real test for the original problem.

* Cleaner logic.

* Make valid base64-encoded value.

* Remove merge conflict.

* Missed a character.

test/data/pipeline/issue2937.json.in

@@ -14,7 +14,7 @@
                 "description": "A second record",
                 "record_id": 43,
                 "user_id": "hobu",
-                "data": "dGhpcyAqdtBpcyBzb21lIHRleHQ="
+                "data": "dGhpcyAqdtBpcyBzb21lIHRlbe=="
             }
         ]
     }