Table: fix table filter (#12539)

packages/table/src/table-column.js

@@ -270,7 +270,7 @@ export default {
       fixed: this.fixed === '' ? true : this.fixed,
       filterMethod: this.filterMethod,
       filters: this.filters,
-      filterable: (this.filters && this.filters.length) || this.filterMethod,
+      filterable: this.filters || this.filterMethod,
       filterMultiple: this.filterMultiple,
       filterOpened: false,
       filteredValue: this.filteredValue || [],

packages/table/src/table-header.js

@@ -124,7 +124,7 @@ export default {
                             : ''
                         }
                         {
-                          (column.filters && column.filters.length) || column.filterMethod
+                          column.filterable
                             ? <span class="el-table__column-filter-trigger" on-click={ ($event) => this.handleFilterClick($event, column) }><i class={ ['el-icon-arrow-down', column.filterOpened ? 'el-icon-arrow-up' : ''] }></i></span>
                             : ''
                         }