Before this commit, an empty line would be shown in the payment forms on
the card of each payment acquirer whose `pre_msg` field was not empty.
This is because displaying this HTML field in a form view and saving it
causes the value `<p><br></p>` to be written on the field, even if it
was left empty. The same issue occurred with the `pending_msg`,
`auth_msg`, `done_msg`, and `cancel_msg` fields that are shown on the
portal of some apps (Sales, Accounting...).
With this commit, the value of these fields is tested before displaying
them. If the value is `<p><br></p>`, the field is not displayed, hence
avoiding to display a blank line.
closesodoo/odoo#84755
X-original-commit: 808cc53bb02b0f1851a2a229bd5235a5fb944408
Signed-off-by: Antoine Vandevenne (anv) <anv@odoo.com>