stream: fix decoded fromList chunk boundary check

Correct `fromList()` in decoded string mode to compare `n` against the
current chunk length, not the buffer array length.
This prevents over-consuming chunks, which can corrupt readable state
and crash with `TypeError` when mixing `setEncoding()` and `read(n)`.
PR-URL: #61884
Reviewed-By: Robert Nagy <ronagy@icloud.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Ilyas Shabi <ilyasshabi94@gmail.com>
Reviewed-By: Gürgün Dayıoğlu <hey@gurgun.day>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Minwoo Jung <nodecorelab@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Ethan Arrowood <ethan@arrowood.dev>

Author: watson

lib/internal/streams/readable.js

@@ -1633,7 +1633,7 @@ function fromList(n, state) {
 n-=str.length;
 buf[idx++]=null;
 }else{
-if(n===buf.length){
+if(n===str.length){
 ret+=str;
 buf[idx++]=null;
 }else{

test/parallel/test-stream2-read-correct-num-bytes-in-utf8.js

@@ -0,0 +1,16 @@
+'use strict';
+
+require('../common');
+constassert=require('assert');
+const{ Readable }=require('stream');
+
+constreadable=newReadable({read(){}});
+readable.setEncoding('utf8');
+
+readable.push('abc');
+readable.push('defgh');
+readable.push(null);
+
+assert.strictEqual(readable.read(5),'abcde');
+assert.strictEqual(readable.read(3),'fgh');
+assert.strictEqual(readable.read(1),null);