move type validation before allocation

Author: mertcanaltin

lib/buffer.js

@@ -639,16 +639,19 @@ Buffer.concat = function concat(list, length) {
   }
 
   validateOffset(length, 'length');
-  const buffer = allocate(length);
-  let pos = 0;
   for (let i = 0; i < list.length; i++) {
-    const buf = list[i];
-    if (!isUint8Array(buf)) {
+    if (!isUint8Array(list[i])) {
       // TODO(BridgeAR): This should not be of type ERR_INVALID_ARG_TYPE.
       // Instead, find the proper error code for this.
       throw new ERR_INVALID_ARG_TYPE(
-        `list[${i}]`, ['Buffer', 'Uint8Array'], buf);
+        `list[${i}]`, ['Buffer', 'Uint8Array'], list[i]);
     }
+  }
+
+  const buffer = allocate(length);
+  let pos = 0;
+  for (let i = 0; i < list.length; i++) {
+    const buf = list[i];
     if (pos + buf.length > length) {
       TypedArrayPrototypeSet(buffer,
                              TypedArrayPrototypeSlice(buf, 0, length - pos),