doc: fix process.stdin example

Fixes: #20503

PR-URL: #25344
Reviewed-By: Colin Ihrig <[email protected]>
Reviewed-By: Matteo Collina <[email protected]>
Reviewed-By: Rich Trott <[email protected]>
Reviewed-By: Luigi Pinca <[email protected]>
Reviewed-By: Anto Aravinth <[email protected]>
Reviewed-By: Franziska Hinkelmann <[email protected]>
Reviewed-By: James M Snell <[email protected]>

Author: addaleax

doc/api/process.md

@@ -1863,8 +1863,9 @@ a [Readable][] stream.
 process.stdin.setEncoding('utf8');
 
 process.stdin.on('readable', () => {
-  const chunk = process.stdin.read();
-  if (chunk !== null) {
+  let chunk;
+  // Use a loop to make sure we read all available data.
+  while ((chunk = process.stdin.read()) !== null) {
     process.stdout.write(`data: ${chunk}`);
   }
 });