Make index bounds consistent with spec

src/index_guesser.c

@@ -7,10 +7,10 @@
 #include "stage2.h"
 
 const size_t MIN_CHOICE = 1;
-const size_t MAX_CHOICE = 256;
+const size_t MAX_CHOICE = UINT8_MAX;
 
 static inline page_t *init_pages(void) {
-    return calloc(MAX_CHOICE, sizeof(page_t));
+    return calloc(MAX_CHOICE + 1, sizeof(page_t));
 }
 
 static inline void flush_all_pages(page_t *pages) {

src/recover_local_secret.c

@@ -10,7 +10,7 @@ const size_t MAX_CHOICE = 'Z' + 1;
 const size_t SECRET_LENGTH = 5;
 
 static inline page_t *init_pages(void) {
-    return calloc(MAX_CHOICE, sizeof(page_t));
+    return calloc(MAX_CHOICE + 1, sizeof(page_t));
 }
 
 static inline void flush_all_pages(page_t *pages) {