[FIX] core: effectively warn on invalid custom views

Since new-api migration of `ir.ui.view`, the method that check views
raises exceptions instead of returning a boolean. Show them as warning.

Related to #14521

openerp/modules/loading.py

@@ -404,8 +404,10 @@ def load_modules(db, force_demo=False, status=None, update_module=False):
         if update_module:
             Views = registry['ir.ui.view']
             for model in registry.models.keys():
-                if not Views._validate_custom_views(cr, SUPERUSER_ID, model):
-                    _logger.warning('Invalid custom view(s) for model %s', model)
+                try:
+                    Views._validate_custom_views(cr, SUPERUSER_ID, model)
+                except Exception as e:
+                    _logger.warning('invalid custom view(s) for model %s: %s', model, tools.ustr(e))
 
         if report.failures:
             _logger.error('At least one test failed when loading the modules.')