Fixed incorrect error path with a GLBuffer of GLBufferType Short

When a GLBuffer of GLBufferType Short is created, a GLBufferException
will be thrown if the buffer is ever written to or read from.  This is
because of a bug in the if-else chain when determining the GLBufferType
of a Buffer.
Merge pull request #12 from game-30/short_buffer

Fixed incorrect error path with a GLBuffer of GLBufferType Short