Fix CHR bug affecting trocq #1387

Job	Run time
Build and test elpi (ubuntu-latest, 4.14.x, dev)	4m 53s
Build and test elpi (windows-latest, 4.14.x, dev)	9m 11s
Build and test elpi (macos-latest, 4.14.x, dev)	6m 49s
Build and test elpi (ubuntu-latest, 5.3.x, fatalwarnings)	4m 21s
Build and test elpi (macos-latest, 5.3.x, dev)	7m 50s
Build and test elpi (windows-latest, 5.3.x, dev)	10m 10s
Aggregate and plot benchmarking data	2m 10s
	45m 24s

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