[FIX] account, usability: hide 'Ask Refund' button when invoice type is already a refund

addons/account/views/account_invoice_view.xml

@@ -219,7 +219,7 @@
                 <header>
                         <button name="action_invoice_open" type="object" states="draft,proforma2" string="Validate" class="oe_highlight" groups="account.group_account_invoice"/>
                         <button name="%(action_account_invoice_payment)d" type="action" states="open" string="Register Payment" groups="account.group_account_invoice" class="oe_highlight"/>
-                        <button name="%(action_account_invoice_refund)d" type='action' string='Ask Refund' groups="account.group_account_invoice" attrs="{'invisible': ['|',('type', '=', 'in_refund'),('state','not in',('open','paid'))]}"/>
+                        <button name="%(action_account_invoice_refund)d" type='action' string='Ask Refund' groups="account.group_account_invoice" attrs="{'invisible': ['|',('type', 'in', ['in_refund','out_refund']),('state','not in',('open','paid'))]}"/>
                         <button name="action_invoice_cancel" type="object" states="draft,proforma2" string="Cancel Bill" groups="account.group_account_invoice"/>
                         <button name="action_invoice_draft" states="cancel" string="Set to Draft" type="object" groups="account.group_account_invoice"/>
                     <field name="state" widget="statusbar" statusbar_visible="draft,open,paid" />