validate block change buffer boundaries for chests

src/procedures.c

@@ -579,6 +579,8 @@ uint8_t makeBlockChange (short x, uint8_t y, short z, uint8_t block) {
     // which naturally appends the chest to the end if a gap isn't found.
     int last_real_entry = first_gap - 1;
     for (int i = first_gap; i <= block_changes_count + 15; i ++) {
+      if (i >= MAX_BLOCK_CHANGES) break; // No more space, trigger failBlockChange
+
       if (block_changes[i].block != 0xFF) {
         last_real_entry = i;
         continue;