LFS Merge Conflict Merges Pointers

## Description

When merging into a branch while using Git LFS, it attempts to merge the LFS pointers together. We then have to manually change the files by removing the pointer we don't want. I would have expected to be prompted with "Take Incoming File" or "Keep Current File" for our LFS files.

## Version

* GitHub Desktop: 1.6.5

* Operating system: Microsoft Windows [Version 10.0.17763.379]

## Steps to Reproduce

1. Create a merge conflict between two LFS files in two different branches.
2. Attempt to merge one branch into the other branch with the merge conflict, and you will see that the conflict was "automatically resolved" when all it did was merge the pointers together.

### Expected Behavior

Be prompted with "Take Incoming File" or "Keep Current File" for LFS files.

### Actual Behavior

The LFS pointers are merged together into one file and breaks the LFS pointer.

## Additional Information

### Logs

[2019-03-26.desktop.production.log](https://github.com/desktop/desktop/files/3009874/2019-03-26.desktop.production.log)