Removing a paragraph between two inline editing macro led to NPE

Steps to reproduce (see the attached gif for more information):

1. Open empty wiki with standard flavour
2. Login as admin
3. Create a new page "Foo"
4. Type "some content" in the editor and enter to add a new line
5. Add a first box with the content "foo"
6. Insert a new line after the box by clicking on the red marker
7. type "bar", select it and insert another box with this content
8. insert a new line between the two boxes by clicking on the red marker
9. type "toto" between the two boxes
10. switch to source mode and back to WYSIWYG
11. double click on "toto" to select it and hit "backward" key to delete it
12. switch again to source mode and back to WYSIWYG: if there was an empty line such as

     {{box}}
    
     bar
     {{/box}}

    in the second box during step 10, repeat 9 to 12 once again.

Expected result:

• The box remains inline editable

Obtained result:

• The second box is not editable anymore, switching again to source shows some HTML and we obtain a NPE in the log trace.

I reproduced the bug with 1.32 but with a bit more steps: I needed to select the second box macro before removing the text in the middle to have the error.