[FIX] account: bank statement usability

- Don't show the button 'Validate' of the statement form when there is no statement line
- In reconciliation widget, use term 'Validate' instead of 'Register Payment' for the use case where the transaction is not reconciled on the spot

addons/account/static/src/js/account_reconciliation_widgets.js

@@ -1868,7 +1868,7 @@ var bankStatementReconciliationLine = abstractReconciliationLine.extend({
                 if (self.st_line.has_no_partner) {
                     createOpenBalance(_t("Choose counterpart"));
                 } else {
-                    displayValidState(false, _t("Register Payment"));
+                    displayValidState(false, _t("Validate"));
                     createOpenBalance(_t("Open balance"));
                 }
             }

addons/account/views/account_view.xml

@@ -428,7 +428,7 @@
                 <header>
                     <field name="all_lines_reconciled" invisible="1" />
                     <button name="%(action_bank_reconcile_bank_statements)d" string="Reconcile" type="action" class="oe_highlight" attrs="{'invisible':['|','|',('all_lines_reconciled','=',True),('line_ids','=',[]),('state', '!=', 'open')]}"/>
-                    <button name="check_confirm_bank" string="Validate" type="object" class="oe_highlight" attrs="{'invisible':['|',('all_lines_reconciled','=',False),('state', '!=', 'open')]}"/>
+                    <button name="check_confirm_bank" string="Validate" type="object" class="oe_highlight" attrs="{'invisible':['|','|',('all_lines_reconciled','=',False),('line_ids','=',[]),('state', '!=', 'open')]}"/>
                     <button name="button_cancel" states="confirm" string="Cancel Statement" type="object"/>
                     <field name="state" widget="statusbar" statusbar_visible="open,confirm"/>
                 </header>