Fix oneshot detection without oneshot_indexes (#426)

Author: igorsereda

CHANGELOG.md

@@ -5,6 +5,12 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog],
 and this project adheres to [Semantic Versioning].
 
+## [Unreleased]
+
+### Fixed
+
+- config: Fixed oneshot detection without `oneshot_indexes`.
+
 ## [5.2.3] - 2022-07-07
 
 ### Added

src/dipdup/config.py

@@ -1278,7 +1278,7 @@ def oneshot(self) -> bool:
         """Whether all indexes have `last_level` field set"""
         syncable_indexes = tuple(c for c in self.indexes.values() if not isinstance(c, HeadIndexConfig))
         oneshot_indexes = tuple(c for c in syncable_indexes if c.last_level)
-        if len(oneshot_indexes) == len(syncable_indexes):
+        if len(oneshot_indexes) == len(syncable_indexes) > 0:
             return True
         return False