required size for the encoding buffer to allocate

This fixes the following error on MacOS
Checking ../../tests/tests-asn1c-compiler/16-constraint-OK.asn1 against ../../tests/tests-asn1c-compiler/16-constraint-OK.asn1.-EFprint-constraints
sed: RE error: illegal byte sequence

The problem is that some of the test files contain non-UTF8 characters

in order to always link with asan and ubsan libraries. Also
this is how the check-converter_example is compiled as well.

fixing the buffer overrun, as this fix was lost with this revert.

This reverts commit 615295a4.

Merging minor security fix (#318)