Bad patch when unstaging a symlink creation at a path that used to be a file

[smashwilson]

To reproduce, in a git repository:

echo "something" > the-file.txt
git add the-file.txt
git commit -m "a commit"

rm the-file.txt
touch target.txt
ln -s target.txt the-file.txt
git add the-file.txt

Now open Atom in the repository, view the staged changes for the-file.txt, and attempt to unstage just the symlink creation.

I've already written a (currently skipped) test for this situation:

github/test/integration/file-patch.test.js

Lines 556 to 580 in f9e3e77

	it.skip('may unstage the symlink creation but not the content deletion', async function() {
	getPatchItem('staged', 'sample.js').find('.github-FilePatchView-metaControls button').simulate('click');
	await clickFileInGitTab('unstaged', 'sample.js');
	await patchContent(
	'unstaged', 'sample.js',
	['const quicksort = function() {', 'deleted', 'selected'],
	[' const sort = function(items) {', 'deleted', 'selected'],
	[' if (items.length <= 1) { return items; }', 'deleted', 'selected'],
	[' let pivot = items.shift(), current, left = [], right = [];', 'deleted', 'selected'],
	[' while (items.length > 0) {', 'deleted', 'selected'],
	[' current = items.shift();', 'deleted', 'selected'],
	[' current < pivot ? left.push(current) : right.push(current);', 'deleted', 'selected'],
	[' }', 'deleted', 'selected'],
	[' return sort(left).concat(pivot).concat(sort(right));', 'deleted', 'selected'],
	[' };', 'deleted', 'selected'],
	['', 'deleted', 'selected'],
	[' return sort(Array.apply(this, arguments));', 'deleted', 'selected'],
	['};', 'deleted', 'selected'],
	);
	assert.isTrue(getPatchItem('unstaged', 'sample.js').find('.github-FilePatchView-metaTitle').exists());
	});
	});
	});