There was a typo that would remove some of the merging in applyFont.

Also there is other issue that have been found:

- whitespace text nodes were removed: depending on structure this can
  remove space between two nodes

- the looping over walkpoint possibly had parent nodes that made no
  sense (eg. container instead of second childNode of container)

- if a text contains normal line return (`<br>`) they are removed when
  changing font size or similar operations

- other instances that the walpoint does not corresponds

In this changeset, the merging is simplified to simply the real previous
font node.

opw-2071930
closes #37345

closes odoo/odoo#37456

X-original-commit: b6e3725f
Signed-off-by: Nicolas Lempereur (nle) <nle@odoo.com>