Fix SVG bug

[whizkid77]

The bug:

1. fileType will sometimes preemptively detect svg files as application/xml before isSvg is called. We want it to be more specific.
2. isSvg requires inspecting the entire file contents, while fileType only requires the first chunk.

The solution:

1. isSvg is more specific, so move it above the fileType call.
2. Use the end event rather than data event for the file stream.

[LinusU]

Sorry that no one ever took a look at this 😢

This was addressed in #103