[FIX] web: form: no "oh snap" dialog after view button clicked

Have a form view with a view button. Make some changes in the form
s.t. the create/write rpc will return an error. Before this commit,
the "oh snap" dialog was displayed, providing 2 choices to the
user: stay here (basically, close the error dialog and do nothing
else) or discard (discard changes, and continue the flow). In this
case, the flow is to do the "call_button" as we clicked on a view
button. It means that if the user clicked on discard, we still
call the method/action, even though the record was invalid (and
maybe not even existing if it was a new record). This can cause
other issues afterwards.

The "oh snap" dialog was designed for navigation flows (e.g. menu,
breadcrumbs...), when the user tries to leave the form view. It
doesn't fit very well with flows involving the current record that
couldn't been saved.

This commit thus prevents the "oh snap" dialog from being displayed
if the save preceeding a call_button fails. The error returned by
the save is simply displayed in a basic dialog that can only be
closed.

opw~3395109

closes odoo/odoo#134783

Signed-off-by: Géry Debongnie <ged@odoo.com>