fix #4122: Fix horizontal scrollbar bug

src/bootstrap-table.css

@@ -306,7 +306,7 @@
 }
 
 /* calculate scrollbar width */
-p.fixed-table-scroll-inner {
+div.fixed-table-scroll-inner {
     width: 100%;
     height: 200px;
 }

src/bootstrap-table.js

@@ -141,7 +141,7 @@
     },
 
     getScrollBarWidth () {
-      if (this.cachedWidth === null) {
+      if (this.cachedWidth === undefined) {
         const $inner = $('<div/>').addClass('fixed-table-scroll-inner')
         const $outer = $('<div/>').addClass('fixed-table-scroll-outer')