Accept Source on conflicted asset creates duplicate, renamed, blueprint asset and makes original unopenable

Accepting source for a conflicted blueprint asset in the merge tool currently creates a new asset *_3 and makes the original name asset unopenable.

Found on:
//UE4/Main CL-3079307
//UE4/Release-4.13 CL-3079129

Found by following test steps for: [Link Removed]

Regression. Will investigate range on request.

1. Make a conflicted asset in P4 (QA look at [Link Removed] for how to do this)
2. Open it in the blueprint editor
3. File > Merge
4. Accept Source