Reject identical source/target in annotation and corpus mappings

Change-Id: I09a410e5d42392680c1ac1c5c9928e3a37aca0cc
diff --git a/mapper/response.go b/mapper/response.go
index e870a29..3ac6b02 100644
--- a/mapper/response.go
+++ b/mapper/response.go
@@ -19,6 +19,10 @@
 		return nil, fmt.Errorf("mapping list with ID %s not found", mappingID)
 	}
 
+	if err := m.validateEffectiveOptions(mappingID, opts); err != nil {
+		return nil, err
+	}
+
 	if m.mappingLists[mappingID].IsCorpus() {
 		return m.applyCorpusResponseMappings(mappingID, opts, jsonData)
 	}