refactor: Use more generated pack functions for NGC savedata.

toxcore/bin_pack.c

@@ -48,7 +48,11 @@ static size_t buf_writer(cmp_ctx_t *ctx, const void *data, size_t count)
             // Buffer too small.
             return 0;
         }
-        memcpy(&bp->bytes[bp->bytes_pos], data, count);
+        if (data == nullptr) {
+            assert(count == 0);
+        } else {
+            memcpy(&bp->bytes[bp->bytes_pos], data, count);
+        }
     }
     bp->bytes_pos += count;
     return count;

toxcore/bin_pack.h

@@ -173,7 +173,7 @@ non_null() bool bin_pack_u64(Bin_Pack *bp, uint64_t val);
 /** @brief Pack an empty array member as a MessagePack nil value. */
 non_null() bool bin_pack_nil(Bin_Pack *bp);
 /** @brief Pack a byte array as MessagePack bin. */
-non_null() bool bin_pack_bin(Bin_Pack *bp, const uint8_t *data, uint32_t length);
+non_null(1) nullable(2) bool bin_pack_bin(Bin_Pack *bp, const uint8_t *data, uint32_t length);
 /** @brief Start packing a custom binary representation.
  *
  * A call to this function must be followed by exactly `size` bytes packed by functions below.