fix executor

Author: GoodDayForSurf

packages/devextreme-themebuilder/src/modules/post-compiler.ts

@@ -31,10 +31,16 @@ export function addInfoHeader(
   const charsetPrefix = /^@charset\s+"utf-8";\s*/i;
   const match = source.match(charsetPrefix);
   if (match) {
-    const rest = source.slice(match[0].length).replace(/^\s*/, '');
-    return appendInfoHeaderAfterBody
-      ? `${encoding}\n${rest}\n${header}`
-      : `${encoding}\n${header}${rest}`;
+    const rest = source.slice(match[0].length).trimStart();
+
+    if (appendInfoHeaderAfterBody) {
+      const joined = `${encoding.trimEnd()}${rest}`.replace(
+        /^(@charset\s+"utf-8";)\s+/i,
+        '$1',
+      );
+      return `${joined}\n${header}`;
+    }
+    return `${encoding}\n${header}${rest}`;
   }
   return `${header}${source}`;
 }