Fix SEGV caused by duplicate memoize hints

HintTypeName was missing the item for the Memoize hint. This causes
SEGV or "(null)" printing by printf on erroring of duplicate memoize
hints.

Add the missing item and a static assertion to check the same kind of
fault.

Reported by ShangBenX <https://github.com/ShangBenX>

pg_hint_plan.c

@@ -216,9 +216,13 @@ static const char *HintTypeName[] = {
 	"leading",
 	"set",
 	"rows",
-	"parallel"
+	"parallel",
+	"memoize"
 };
 
+StaticAssertDecl(sizeof(HintTypeName) / sizeof(char *) == NUM_HINT_TYPE,
+				 "HintTypeName and HintType don't match");
+
 /* hint status */
 typedef enum HintStatus
 {