More robust metadata handling if we don't have field_values

frontend/src/lib/schema_metadata.js

@@ -149,7 +149,7 @@ function equivalentArgument(field, table) {
     }
 
     if (isCategory(field)) {
-        if (field.id in table.field_values && table.field_values[field.id].length > 0) {
+        if (table.field_values && field.id in table.field_values && table.field_values[field.id].length > 0) {
             let validValues = table.field_values[field.id];
             // this sort function works for both numbers and strings:
             validValues.sort((a, b) => a === b ? 0 : (a < b ? -1 : 1));