Syntax highlighting is lost when src_block is indented

[jjnilton]

To reproduce, write an indented src_block restclient.

Example:

* ob-restclient parent
#+begin_src restclient
GET http://example.com
#+end_src

#+begin_src python
print("hello world")
#+end_src

  - [ ] restclient block loses its syntax highlight
     #+begin_src restclient
     GET http://example.com
     #+end_src
     
     #+begin_src python
     print("hello world")
     #+end_src