Do not rely on invoice state to compute reconciliation lines

Closes #12864
(grafted from 94018bd6531aa5943e5044d925b24c04fc5ecb8c)

--HG--
branch : 6.0

modules/account_invoice/invoice.py

@@ -723,7 +723,7 @@ class Invoice(Workflow, ModelSQL, ModelView, TaxableMixin):
         return lines
 
     def get_reconciliation_lines(self, name):
-        if self.state != 'paid':
+        if not self.move:
             return
         lines = set()
         for line in self.move.lines: