Fix crash seen in ROOT-5570.
Fix crash seen in ROOT-5570.

root-mirror/cling,perovic/cling,marsupial/cling,karies/cling,root-mirror/cling,karies/cling,root-mirror/cling,perovic/cling,perovic/cling,perovic/cling,root-mirror/cling,root-mirror/cling,karies/cling,perovic/cling,marsupial/cling,root-mirror/cling,marsupial/cling,marsupial/cling,karies/cling,marsupial/cling,marsupial/cling,karies/cling,karies/cling