fix(ui): table sort issue (quasarframework#5670)

* fix(ui): table sort issue

* Update table-sort.js

Author: hawkeye64

ui/src/components/table/table-sort.js

@@ -7,7 +7,7 @@ export default {
       type: Function,
       default (data, sortBy, descending) {
         const col = this.columns.find(def => def.name === sortBy)
-        if (col === null || col.field === void 0) {
+        if (col === void 0 || col.field === void 0) {
           return data
         }