Fix memory corruption in unicode:characters_to_binary

`term_binary_data_size_in_terms` is dangerous since it doesn't account
for binary header size, so a memory corruption is almost certain.

Signed-off-by: Davide Bettio <davide@uninstall.it>

CHANGELOG.md

@@ -28,6 +28,7 @@ instead
 
 - ESP32: content of `boot.avm` partition is not truncated anymore
 - ESP32: Fixed gpio:set_int` to accept any pin, not only pin 2
+- Fix memory corruption in `unicode:characters_to_binary`
 
 ## [0.6.4] - 2024-08-18
 

src/libAtomVM/nifs.c

@@ -4616,7 +4616,7 @@ static term nif_unicode_characters_to_binary(Context *ctx, int argc, term argv[]
     if (UNLIKELY(conv_result == UnicodeBadArg)) {
         RAISE_ERROR(BADARG_ATOM);
     }
-    size_t needed_terms = term_binary_data_size_in_terms(len);
+    size_t needed_terms = term_binary_heap_size(len);
     if (UNLIKELY(conv_result == UnicodeError || conv_result == UnicodeIncompleteTransform)) {
         needed_terms += TUPLE_SIZE(3) + rest_size;
     }