Adjust overstrong nbtree skip array assertion.

Make an nbtree array preprocessing assertion account for scans that add
fewer skip arrays than initially expected due to preprocessing finding
an unsatisfiable array qual.

Oversight in commit 92fe23d9.

Author: Peter Geoghegan <pg@bowt.ie>
Reported-By: Mark Dilger <mark.dilger@enterprisedb.com>
Discussion: https://postgr.es/m/CAHgHdKtQMhHy5qcB3KqCcGiW-Rp8P7KzUFRa9ZMKUiv6zen7LQ@mail.gmail.com

src/backend/access/nbtree/nbtpreprocesskeys.c

@@ -1856,7 +1856,7 @@ _bt_preprocess_array_keys(IndexScanDesc scan, int *new_numberOfKeys)
 		numArrayKeyData++;		/* keep this scan key/array */
 	}
 
-	Assert(numSkipArrayKeys == 0);
+	Assert(numSkipArrayKeys == 0 || !so->qual_ok);
 
 	/* Set final number of equality-type array keys */
 	so->numArrayKeys = numArrayKeys;