[FIX] payment: py3 error payment icon save

Code to thumbnail payment icon image had an error for python3 because
from RPC the image would be a text string instead of an expected
bytestring.

This change accepts both and made another small fix in the view since
image_medium doesn't exist (and image is already thumbnailed).

A third fix was that removing an image caused an error.

opw-803722
closes #22088

addons/payment/models/payment_acquirer.py

@@ -437,15 +437,17 @@ class PaymentIcon(models.Model):
     @api.model
     def create(self, vals):
         if 'image' in vals:
-            vals['image_payment_form'] = image_resize_image(vals['image'], size=(45,30))
-            vals['image'] = image_resize_image(vals['image'], size=(64,64))
+            image = ustr(vals['image'] or '').encode('utf-8')
+            vals['image_payment_form'] = image_resize_image(image, size=(45,30))
+            vals['image'] = image_resize_image(image, size=(64,64))
         return super(PaymentIcon, self).create(vals)
 
     @api.multi
     def write(self, vals):
         if 'image' in vals:
-           vals['image_payment_form'] = image_resize_image(vals['image'], size=(45,30))
-           vals['image'] = image_resize_image(vals['image'], size=(64,64))
+            image = ustr(vals['image'] or '').encode('utf-8')
+            vals['image_payment_form'] = image_resize_image(image, size=(45,30))
+            vals['image'] = image_resize_image(image, size=(64,64))
         return super(PaymentIcon, self).write(vals)
 
 class PaymentTransaction(models.Model):

addons/payment/views/payment_views.xml

@@ -416,7 +416,7 @@
             <field name="arch" type="xml">
                 <form string="Payment Icon">
                     <sheet>
-                        <field name="image" widget="image" class="oe_avatar" options='{"preview_image": "image_medium"}'/>
+                        <field name="image" widget="image" class="oe_avatar"/>
                         <div class="oe_title">
                             <h1><field name="name" placeholder="Name"/></h1>
                         </div>