Fix and test for Issue #41

When `buffers` is an array of one buffer of zero length (falsey), this reduce operation ends up producing the string "0" in the output buffer. I couldn't find any reason the reduce operation needed to test either `left` or `right`, since `left` will always be a Number, and both places MergeBuffers is used it `buffers` elements will always have `length`. It still passes the entire test suite with this patch in place.