EZP-31084: Fix infinitive loop in cache emptyTrash()

[andrerom]

Question	Answer
JIRA issue	EZP-31084
Bug/Improvement	yes
Target version	7.5
BC breaks	no
Tests pass	yes
Doc needed	no

Attempt to fix issue found in #2847 by @mnocon.

[mnocon]

Looks good now! I've also prepared some benchmarking with the Command I've mentioned in #2847 to compare the behaviour of TrashService::emptyTrash()

After: #2847

(number of items in trash -> Time in ms, Memory in Bytes)
100 -> Time: 1032, Memory: 46661632
150 -> Time: 1025.8, Memory: 46661632
500 -> Time: 3216.9, Memory: 46661632
2000 -> Time: 12527.2, Memory: 46661632
5000 -> Time: 30693.8, Memory: 48758784
9000 -> Time: 56136.7, Memory: 50855936

Before:

(number of items in trash -> Time in ms, Memory in Bytes)
100 -> Time: 597.1, Memory: 46661632
150 -> Time: 1010.4, Memory: 46661632
500 -> Time: 2850.8, Memory: 46661632
2000 -> Time: 12138.2, Memory: 50855936
5000 -> Time: 31895.1, Memory: 61341696
9000 -> Time: 51164.7, Memory: 69730304

I'd say there isn't much of a time difference, but the memory footprint definitely looks lower when there are more items in Trash.

[andrerom]

Nice one @mnocon, good to see the growth is noticeably slower.

You should btw expect somewhat larger difference on Admin trash view once we fix the remaining issues, as that loads full API objects and not just SPI objects which is the case here.