F fix assure in list

Summary

For https://gitlab.indiscale.com/caosdb/internal/all/-/issues/530 (or https://gitlab.com/caosdb/caosdb-advanced-user-tools/-/issues/40). Fixes a specific bug whereby assure_object_is_in_list would fail on update when adding an object to an initially empty list.

Focus

The fix is only two lines in cfood.py and there is a new integration test reproducing the problem in https://gitlab.com/caosdb/caosdb-advanced-user-tools/-/issues/40.

Test Environment

Integration test should be sufficient, but feel free to experiment manually with similar cases (don't forget to set the global guard level to UPDATE if you want to test it manually.)

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integrationtests/extroot/Software/2010_TestSoftware/2019-02-03_v0.1/README.md

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 responsible: Responsible, Only
-description: 	A description of this example analysis.
+description: 	A description of another example analysis.
 
 sources:
 - file:	"/ExperimentalData/2010_TestProject/2019-02-03/*.dat"