Do not substract 1 if the buffer length is 0.

Start value should be lower or equal with end value. When buffer length is 0 (empty file), this snippet was throwing an error. After this change we substract one unit if the buffer length is not 0.

lib/node-static.js

@@ -361,7 +361,7 @@ Server.prototype.stream = function (pathname, files, buffer, startByte, res, cal
                 flags: 'r',
                 mode: 0666,
                 start: startByte,
-                end: startByte + buffer.length - 1
+                end: startByte + (buffer.length ? buffer.length - 1 : buffer.length)
             }).on('data', function (chunk) {
                 // Bounds check the incoming chunk and offset, as copying
                 // a buffer from an invalid offset will throw an error and crash