[BUG] org-babel-tangle fails with :comments org and missing comment

[BUG] org-babel-tangle fails with :comments org and missing comment

[Daniele Pizzolli]

Hello,

this is the last bug report about the errors I encountered while trying
to write a presentation with org-mode few days ago.  Let me know if you
need further info on this or previous reports.

The following snippet will make M-x org-babel-tangle to fail and write
a partial demo.sh because of ":comments org" and no comment between
the two first source blocks.

I see no reason for this failure.  Maybe a warning about the missing
comment is a nice to have, but a failure because of a missing comment
does not make sense to me.

#+PROPERTY: header-args:sh :tangle demo.sh :comments org

* tangle this file to get an error

Org-mode version 8.3beta (release_8.3beta-866-gc1da4d @
/home/vagrant/.emacs.d/el-get/org-mode/lisp/)

Let's see the difference between two commands:

#+BEGIN_SRC sh
ls | wc
#+END_SRC

#+BEGIN_SRC sh
ls | wc -l
#+END_SRC

comment for next block:

#+BEGIN_SRC sh
ls -a | wc -l
#+END_SRC

Thanks in advance,
Daniele