Difference in last line does not get handled

### Bug Description
See title.
`getChangedLines()` does return the correct line numbers.

### Steps To Reproduce
Put a difference in the last line.

### Expected Behavior
The change in the last line should be displayed when calling `getDiff()` or `renderDiff()`.

### Possible Solution
`$captureLine` only gets pushed onto `$return` when a line is equal. When the last line is reached and differs, the for loop is already ending and the capture buffer is not checked anymore.

Seems to work when putting a copy of the `if ($captureBuffer !== [])` block before the `return`.

Inspect the implementation of getDiff() and renderDiff(), focusing on how the capture buffer is handled after the final line. Reproduce a difference on the last line and verify that the resulting diff includes it; the issue is done when both methods display that final-line change.

索引モデルが issue の本文から書いたものです。