CATROID-1479 Test: testFunctionDeletion fails

[Rawbat]

The test was failing because the back button in the formula editor was not set active again after exiting the function menu. I fixed this adding a call to set it active if necessary. Now the behaviour should be as intended and the test passes.

https://jira.catrob.at/browse/CATROID-1479

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[reichli]

Looks good! Thank you :)