stream: improve read() performance further

lib/internal/streams/buffer_list.js

@@ -71,19 +71,19 @@ module.exports = class BufferList {
 
   // Consumes a specified amount of bytes or characters from the buffered data.
   consume(n, hasStrings) {
-    var ret;
-    if (n < this.head.data.length) {
+    const data = this.head.data;
+    if (n < data.length) {
       // `slice` is the same for buffers and strings.
-      ret = this.head.data.slice(0, n);
-      this.head.data = this.head.data.slice(n);
-    } else if (n === this.head.data.length) {
+      const slice = data.slice(0, n);
+      this.head.data = data.slice(n);
+      return slice;
+    }
+    if (n === data.length) {
       // First chunk is a perfect match.
-      ret = this.shift();
-    } else {
-      // Result spans more than one buffer.
-      ret = hasStrings ? this._getString(n) : this._getBuffer(n);
+      return this.shift();
     }
-    return ret;
+    // Result spans more than one buffer.
+    return hasStrings ? this._getString(n) : this._getBuffer(n);
   }
 
   first() {