SVGR fails silently when there is no imports and exports in provided template

[xcrzx]

🐛 Bug Report

Skipping imports and exports in the template provided to @svgr/core config result in empty output.
If I add either imports or exports to the template everything work as expected.

To Reproduce

const result = await svgr(
    '<svg width="16" height="16" xmlns="http://www.w3.org/2000/svg"><path d="M3 3.8V3h11v.8l-4 4.8V14l-3-1.5V8.6z" fill-rule="evenodd"/></svg>', 
    {
     template: ({ template }, opts, { jsx }) => template.ast`${jsx};`,
});
console.log(result) // Empty string

Expected behavior

Expect result to contain jsx code.

Link to repl or repo (highly encouraged)

https://github.com/xcrzx/svgr-template-issue

Run npx envinfo --system --binaries --npmPackages @svgr/core,@svgr/cli,@svgr/webpack,@svgr/rollup --markdown --clipboard

Paste the results here:

## System:
 - OS: macOS 10.14
 - CPU: x64 Intel(R) Core(TM) i7-7820HQ CPU @ 2.90GHz
 - Memory: 127.24 MB / 16.00 GB
 - Shell: 5.3 - /bin/zsh
## Binaries:
 - Node: 11.0.0 - ~/.nvm/versions/node/v11.0.0/bin/node
 - Yarn: 1.12.1 - /usr/local/bin/yarn
 - npm: 6.4.1 - ~/.nvm/versions/node/v11.0.0/bin/npm
 - Watchman: 4.9.0 - /usr/local/bin/watchman