Merge pull request #7373 from weibangtuo/fix/7372

fix/7353  fix _toggleColumn exception when column size change

src/bootstrap-table.js

@@ -2859,7 +2859,7 @@ class BootstrapTable {
   }
 
   _toggleColumn (index, checked, needUpdate) {
-    if (index === -1 || this.columns[index].visible === checked) {
+    if (index === undefined || this.columns[index].visible === checked) {
       return
     }
     this.columns[index].visible = checked