Fix: When using a scrolling table and there was a x-scroll offset when entering the floating mode, the x-scroll wouldn't be applied.

https://datatables.net/forums/discussion/81476

Author: AllanJard

js/dataTables.fixedHeader.js

@@ -439,6 +439,8 @@ $.extend(FixedHeader.prototype, {
 itemDom.floating.append(itemElement);
 
 this._widths(itemDom);
+
+return scrollLeftUpdate;
 }
 },
 
@@ -581,7 +583,7 @@ $.extend(FixedHeader.prototype, {
 else if (mode === 'in') {
 // Remove the header from the real table and insert into a fixed
 // positioned floating table clone
-this._clone(item, forceChange);
+let scrollLeftUpdate = this._clone(item, forceChange);
 
 // Get useful position values
 var scrollOffset = scrollBody.offset();
@@ -625,6 +627,7 @@ $.extend(FixedHeader.prototype, {
 });
 
 importantWidth(position.width);
+scrollLeftUpdate();
 
 if (item === 'footer') {
 itemDom.floating.css('top', '');