Use raw mode on custom or broken sieve file (#3387)

* Use raw mode on custom or broken sieve file

* Fixed display of sieve filters when none are active

* Updated test

modoboa/core/checks.py

@@ -1,4 +1,4 @@
-from django.db.utils import ProgrammingError
+from django.db.utils import ProgrammingError, OperationalError
 from django.core.checks import register, Info, Warning
 from django.conf import settings
 from django.utils.translation import gettext as _
@@ -53,7 +53,7 @@ def check_password_hasher(app_configs, **kwargs):
     msgs = []
     try:
         hasher = check_for_deprecated_password_schemes()
-    except ProgrammingError:
+    except (ProgrammingError, OperationalError):
         # This is probably a fresh install...
         return []
     if hasher: