added fr.is_good() to check existence of alleged files

csst_common/file_recorder.py

@@ -97,3 +97,7 @@ class FileRecorder(list):
         return f"{len(self)} alleged, " \
                f"{len(self) - sum(self.to_table()['existence'])} missing, " \
                f"{sum(self.to_table()['existence'])} to db"
+
+    def is_good(self):
+        """ Check if all alleged files exist. """
+        return all(self.to_table()['existence'])