Viewing a file at an ambiguous ref causes the wrong content to be displayed.

Issue Summary

Incorrect content is displayed when a file view is requested at an ambiguous ref

Steps to Reproduce

1. Create a tag that has the same name as a branch e.g. `git tag master`
2. Make a change to a file that already exists on master
3. Push the change to Bitbucket
4. View the file in Bitbucket source view

Expected Results

View the file content on the branch that was requested

Actual Results

The file content at tag that has the same name as the branch.

Workaround

Delete ambiguous refs.