The diff of the first line is wrong

[mbork]

When diffing two files where the first line was changed, the "old" ("left") one shows an empty line instead. Here is a minimal (or at least fairly small) example:

"old file":

const React = require('react');
console.log('hello world');

"new" file:

import React, {useState} from 'react';
console.log('hello world');

Result of difft old.js new.js:

new.js --- 1/1 --- JavaScript
.                                                                                              1 import React, {useState} from 'react';
2 console.log('hello world');                                                                  2 console.log('hello world');

Note: this looks like it could be connected (or the same) as #90.

I observed this in v0.15.0, but I'm almost sure the output was correct in v0.11.0 (the previous one I used).