Issue Summary

The "Files changed" tab in the new Pull request UI doesn't show the number of file changed when the Pull request first loaded

Steps to Reproduce

1. Enable the "New pull request experience" lab feature by visiting https://bitbucket.org/account/settings/features/
2. Open any Pull request
3. Observe the number of files changed in the Pull request in "Files changed" tab

Expected Results

The "Files changed" tab should display the number of files changed in the Pull request

Actual Results

The "Files changed" tab doesn't show any number of files changed in the Pull request

Workaround

Click on the "Files changed" tab and then after that "Files changed" tab will start showing the number of files changed in the Pull request