Error: Stream yields empty buffer

node: v7.10.0
npm: v5.0.0

```
❯ smartcrop --width 100 --height 100 avatar.jpg
Error: Stream yields empty buffer
at Socket. (/usr/local/lib/node_modules/smartcrop-cli/node_modules/gm/lib/command.js:57:17)
at emitNone (events.js:91:20)
at Socket.emit (events.js:188:7)
at endReadableNT (_stream_readable.js:975:12)
at _combinedTickCallback (internal/process/next_tick.js:80:11)
at process._tickCallback (internal/process/next_tick.js:104:9)
```

Start by reproducing the issue with `smartcrop --width 100 --height 100 avatar.jpg` on the reported Node.js and npm versions. Use the stack trace location in `smartcrop-cli/node_modules/gm/lib/command.js` as the initial investigation point, then trace back to the CLI entry point; done means the command completes without the empty-buffer error.

Written by the indexing model from the issue text.