Crash (String index out of range) when trying to view a repo that is already inside a repo

[GoogleCodeExporter]

What steps will reproduce the problem?
1. Install gitiles (ant and buck)
2. cd repo1 # where there is repo1/repo2, for example, cd gitiles, where 
bucklets is repo2
3. Run /path/to/gitiles/tools/run_dev.sh
4. Open localhost:8080

What is the expected output? What do you see instead?
Expected to see repo2. Instead:
Error 500:     java.lang.StringIndexOutOfBoundsException: String index out of 
range: -1

What version of the product are you using? On what operating system?
Commit 71eeed1

Please provide any additional information below.
- Mac
- Looks similar to issue 101.
- Note that when I tried with repo1/folder/repo2 and cd repo1/folder, it worked.

Original issue reported on code.google.com by lpromero@chromium.org on 8 Mar 2016 at 6:04