fix(性能测试): 修复性能测试jmx中脚本空格被过滤掉的问题

--bug=1010634 --user=刘瑞斌 【性能测试】场景转性能测试后，脚本里少了个空格 https://www.tapd.cn/55049933/s/1110317

backend/src/main/java/io/metersphere/performance/parse/EngineSourceParserFactory.java

@@ -59,7 +59,11 @@ public class EngineSourceParserFactory {
         ) {
             // 删除空白的行
             List<Node> nodes = document.selectNodes("//text()[normalize-space(.)='']");
-            nodes.forEach(node -> node.setText(""));
+            nodes.forEach(node -> {
+                if (node.getText().contains("\n")) {
+                    node.setText("");
+                }
+            });
 
             XMLWriter xw = new XMLWriter(out, format);
             xw.setEscapeText(IS_TRANS);