Handle /app_profiler/ index path with slash in speedscope remote viewer middleware

[shioyama]

I was confused when I tried accessing /app_profiler/ and got the following error:

Puma caught this error: ArgumentError (ArgumentError)
/usr/local/bundle/bundler/gems/app_profiler-7017e16d966a/lib/app_profiler/viewer/speedscope_remote_viewer/middleware.rb:33:in `show'
/usr/local/bundle/bundler/gems/app_profiler-7017e16d966a/lib/app_profiler/viewer/speedscope_remote_viewer/base_middleware.rb:31:in `call'
...

The problem is that the middleware only accepts /app_profiler and not /app_profiler/ as the path, the latter is treated as a path to an actual profiler with a name value of "", which crashes with the exception above.

I just made a change to optionally accept /app_profiler/ as well.