[FIX] ir.model.data: verify record exists in _update_dummy

When a stale XML ID exists in the database, `_update_dummy()`
must consider it as missing entirely, and the next call
to `_update()` will take care of cleaning up the old XML ID.

Failing to do so for `noupdate` records means the `_update`
will never happen, and as soon as another record is created
or updated with a relationship to that stale XML ID, it will
plainly crash the installation/update.

openerp/addons/base/ir/ir_model.py

@@ -985,11 +985,15 @@ class ir_model_data(osv.osv):
     def _update_dummy(self,cr, uid, model, module, xml_id=False, store=True):
         if not xml_id:
             return False
+        id = False
         try:
-            id = self.read(cr, uid, [self._get_id(cr, uid, module, xml_id)], ['res_id'])[0]['res_id']
-            self.loads[(module,xml_id)] = (model,id)
-        except:
-            id = False
+            # One step to check the ID is defined and the record actually exists
+            record = self.get_object(cr, uid, module, xml_id)
+            if record:
+                id = record.id
+                self.loads[(module,xml_id)] = (model,id)
+        except Exception:
+            pass
         return id
 
     def clear_caches(self):