I tried your code and I get the same problem.
Google Books
Bluefire Reader
The thing is that, Google Books doesn’t use the height and width specified inside the svg image, and use only those in the ePub. So if nothing is written, the image will be very tiny. And if only one value is written, than the other one will create problem (big white space). So the solution is to specifiy both the width and height in both the svg image AND the ePub, but this is time consuming if you have to process a lot of svg images!