docs: better handle parsing errors in file name

Author: GrosSacASac

README.md

@@ -631,7 +631,7 @@ file system.
 form.on('fileBegin', (formName, file) => {
     // accessible here 
     // formName the name in the form (<input name="thisname" type="file">)
-    // file.name (http filename)
+    // file.name http filename or null if there was a parsing error
     // file.path default pathnme as per options.uploadDir and options.filename
     // file.path = CUSTOM_PATH // to change the final path
 });

examples/with-http.js

@@ -8,7 +8,18 @@ const server = http.createServer((req, res) => {
     // parse a file upload
     const form = formidable({ multiples: true });
 
+    form.on("fileBegin", (formName, file) => {
+      if (file.name === null) {
+        file.name = "invalid-characters"
+      }
+    })
     form.parse(req, (err, fields, files) => {
+      if (err) {
+        console.error(err);
+        res.writeHead(400, { 'Content-Type': 'text/plain' });
+        res.end("Bad Request");
+        return;
+      }
       res.writeHead(200, { 'Content-Type': 'application/json' });
       res.end(JSON.stringify({ fields, files }, null, 2));
     });