babel-plugin-server: non-identifier expression as JSX element name

[shuhei]

babel-plugin-server prerenders <undefined><undefined> given a non-identifier expression as JSX element name.

A minimum test case:

$ echo '<Foo.Bar />;' | ./node_modules/.bin/babel --plugins ./src/transform/server
({
  __prerendered__: "dom",
  segments: ["<undefined", 1, "></undefined>"]
});