buffer: use strict equality comparison

[JungMinu]

There is no type-conversion to be done because both parameters are already the same type.
Therefore, the === operator should be used for better performance.

[targos]

obj == null is equivalent to strictly comparing against null and undefined. The change you are proposing makes us lose the obj === undefined part. Therefore line 127 would throw if undefined is passed to the Buffer constructor.

[targos]

It should be caught by this test. Did you run make test ?

[JungMinu]

@targos Sorry, It was a mistake