race condition when redacted deleted way is referenced by relations

[tyrasd]

Describe the bug
When a relation (like relation/10215810) references a way which has only one "deleted" version after redactions (like way/687863323), the CellIterator hits a race condition here.

To Reproduce

    OSMEntitySnapshotView
          .on(oshdb).keytables(keytables)
          .areaOfInterest(new OSHDBBoundingBox(44.0,46.0,44.5,46.5))
          .timestamps("2020-12-01")
          .osmType(OSMType.RELATION)
          .osmEntityFilter(e -> e.getId() == 10215810L)
          .count();

alternatively triggered via ohsome API:

curl -X GET "https://api.ohsome.org/v1/elements/count?bboxes=44.0%2C46.0%2C44.5%2C46.5&filter=type%3Arelation%20and%20id%3A10215810&format=json&time=2014-01-01%2F2020-01-01%2FP1Y"

Expected behavior
no error should be triggered

Error messages, logs, screenshots

java.util.NoSuchElementException
	at java.base/java.util.ArrayList$Itr.next(ArrayList.java:1000)
	at org.heigit.bigspatialdata.oshdb.osh.OSHEntities._getModificationTimestamps(OSHEntities.java:459)
	at org.heigit.bigspatialdata.oshdb.osh.OSHEntities.getModificationTimestamps(OSHEntities.java:312)
	at org.heigit.bigspatialdata.oshdb.osh.OSHEntities.getModificationTimestamps(OSHEntities.java:246)
	at org.heigit.bigspatialdata.oshdb.util.celliterator.CellIterator.lambda$iterateByContribution$7(CellIterator.java:485)

System (please complete the following information):

• OSHDB Version: 0.7.0-SNAPSHOT, 0.6.0, 0.5.10

Additional context
We should probably provide a backport for this bug fix for 0.6 and 0.5.