refactor: optimize snippet markdown plugin code (#2580)

src/node/markdown/plugins/snippet.ts

@@ -145,12 +145,21 @@ export const snippetPlugin = (md: MarkdownIt, srcDir: string) => {
     // @ts-ignore
     const [src, regionName] = token.src ?? []
 
-    if (src) {
+    if (!src) return fence(...args)
+
     if (loader) {
       loader.addDependency(src)
     }
+
     const isAFile = fs.lstatSync(src).isFile()
-      if (fs.existsSync(src) && isAFile) {
+    if (!fs.existsSync(src) || !isAFile) {
+      token.content = isAFile
+        ? `Code snippet path not found: ${src}`
+        : `Invalid code snippet option`
+      token.info = ''
+      return fence(...args)
+    }
+
     let content = fs.readFileSync(src, 'utf8')
 
     if (regionName) {
@@ -161,20 +170,13 @@ export const snippetPlugin = (md: MarkdownIt, srcDir: string) => {
         content = dedent(
           lines
             .slice(region.start, region.end)
-                .filter((line: string) => !region.regexp.test(line.trim()))
+            .filter((line) => !region.regexp.test(line.trim()))
             .join('\n')
         )
       }
     }
 
     token.content = content
-      } else {
-        token.content = isAFile
-          ? `Code snippet path not found: ${src}`
-          : `Invalid code snippet option`
-        token.info = ''
-      }
-    }
     return fence(...args)
   }