Fix: New line wasn't being used between body and footer for CSV and Copy inline and exports

Fix: `footer` could show undefined if the title `span` was replaced

https://datatables.net/forums/discussion/78342

Author: AllanJard

js/buttons.html5.js

@@ -333,7 +333,7 @@ var _exportData = function (dt, config) {
 	}
 
 	return {
-		str: header + body.join(newLine) + footer,
+		str: header + body.join(newLine) + newLine + footer,
 		rows: body.length
 	};
 };

js/dataTables.buttons.js

@@ -2584,11 +2584,17 @@ var _exportData = function (dt, inOpts) {
 				.indexes()
 				.map(function (idx) {
 					var el = dt.column(idx).footer();
-					return config.format.footer(
-						el ? $('.dt-column-title', el).html() : '',
-						idx,
-						el
-					);
+					var val = '';
+
+					if (el) {
+						var inner = $('.dt-column-title', el);
+
+						val = inner.length
+							? inner.html()
+							: $(el).html();
+					}
+
+					return config.format.footer(val, idx, el);
 				})
 				.toArray()
 		: null;