buffer: zero-length buffers shouldn't be slab-backed

lib/buffer.js

@@ -199,8 +199,9 @@ function coerce(length) {
 }
 
 
-// Buffer
+var zeroBuffer = new SlowBuffer(0);
 
+// Buffer
 function Buffer(subject, encoding, offset) {
   if (!(this instanceof Buffer)) {
     return new Buffer(subject, encoding, offset);
@@ -242,13 +243,18 @@ function Buffer(subject, encoding, offset) {
       this.parent = new SlowBuffer(this.length);
       this.offset = 0;
 
-    } else {
+    } else if (this.length > 0) {
       // Small buffer.
       if (!pool || pool.length - pool.used < this.length) allocPool();
       this.parent = pool;
       this.offset = pool.used;
       pool.used += this.length;
       if (pool.used & 7) pool.used = (pool.used + 8) & ~7;
+
+    } else {
+      // Zero-length buffer
+      this.parent = zeroBuffer;
+      this.offset = 0;
     }
 
     // Treat array-ish objects as a byte array.