Redirect of branch url incorrectly converts branch names to lower case (BB-10034)

Steps to reproduce:

1. On a given account "abc" and repo "def", create a branch with some UPPER case characters, e.g., "DEV-1-new-issue". The branch url would looks like: https://bitbucket.org/abc/def/branch/DEV-1-new-issue
2. Rename the account name from "abc" to "Abc" (or anything else)
3. Visit the original branch url

Expected: be redirected to https://bitbucket.org/Abc/def/branch/DEV-1-new-issue\\
Actual: redirected to https://bitbucket.org/Abc/def/branch/dev-1-new-issue (note the lower case "dev") and got 404