Speed up the exact match operation.

Only call strcmp() once, when a node is reached that must be either a
hit or a miss.

src/patricia.c

@@ -236,13 +236,16 @@ PT_Lookup(const struct pt_y * const restrict root,
 	  char * const restrict * const restrict strings,
 	  const char * const restrict subject)
 {
+	const struct pt_y *y = root;
 	size_t len;
 
 	AN(strings);
 	AN(subject);
+	if (root == NULL)
+		return UINT_MAX;
 	len = strlen(subject);
 
-	for (const struct pt_y *y = root; y != NULL;) {
+	for (;;) {
 		unsigned char b;
 		size_t l;
 
@@ -250,13 +253,17 @@ PT_Lookup(const struct pt_y * const restrict root,
 		l = y->off + y->len;
 		if (l > len)
 			return UINT_MAX;
-		if (l == len && strcmp(subject, strings[y->idx]) == 0)
-			return y->idx;
+		if (l == len && strings[y->idx][l] == '\0')
+			break;
 		b = (y->bitmask & subject[l]) != 0;
 		assert(b < 2);
+		if (y->leaf[b] == NULL)
+			return UINT_MAX;
 		y = y->leaf[b];
 	}
 
+	if (strcmp(subject, strings[y->idx]) == 0)
+		return y->idx;
 	return (UINT_MAX);
 }