[O] Bug: org-toggle-heading breaks with double colon '::' list items.

[Leo Ufimtsev]

Hello, 

If I have a list with colons like:

- List a ::
  Cheese 
  Bannana 
- List b :: 
  Pineapples 
  Tomatoes 

If I then select the entire list and call org-toggle-headings, then I would 
*expect* this:

* List a 
  Cheese 
  Bannana
* List b 
  Pineapples 
  Tomatoes

But instead the first item is placed on the same line as the heading:
* List a Cheese 
  Bannana
* List b Pineapples 
  Tomatoes

This is happens only with items that have colons. A workaround is not to use 
colons or add a dot after the colons, e.g
- List a :: .
  Cheese 

The use case is that I often start making lists, but as things grow turn them 
into headings.

I'm on Emacs 25.0.50.4 (~3 weeks old) and my org-mode is from this morning 
(8.3beta). 

Please advise.

Thank you

Leo