Fix for DAV response processing (avoid segfault) (Fixes BUGZ-4148)
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This merge request is automatically cherrypicked from !1679 (merged) from source branch https://source.coderefinery.org/aleksandr.konstantinov/arc/-/tree/dav_parse_fix orginally made by @aleksandr.konstantinov .
The original MR went to branch: https://source.coderefinery.org/nordugrid/arc/-/tree/next
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Bug was causing A-REX coredump due to access to undefined iterator (most probably).