[FIX] web_editor: delete behavior before table

Before this commit:

* A delete at the end of an empty block just before a table (unbreakable), nothing happened.

After this commit:

* A delete at the end of an empty block just before an unbreakable block, the empty paragraph should be removed and the selection put at the beginning of the unbreakable block.

task-3186679
task-3252775

closes odoo/odoo#125211

Signed-off-by: David Monjoie (dmo) <dmo@odoo.com>