fix: skip invalid code block metadata without key-value pairs (#561)

This ensures compatibility with transformers like `transformerMetaHighlight`, which may include metadata without key-value formatting.

Previously, metadata entries without an = would cause [key, value] to be undefined, potentially introducing invalid entries into the map. We now skip such entries to ensure only valid key-value pairs are parsed.

src/utils/transformers/fileName.js

@@ -29,6 +29,7 @@ export const transformerFileName = ({
 
     for (const item of raw) {
       const [key, value] = item.split("=");
+      if (!key || !value) continue;
       metaMap.set(key, value.replace(/["'`]/g, ""));
     }