Add length check to Hmac_UpdateFinal_CT to prevent build error

[padelsbach]

Description

Fix for the following compile issue:

In function ‘Hmac_UpdateFinal_CT’,
    inlined from ‘TLS_hmac’ at src/tls.c:1340:23:
src/tls.c:1072:50: error: writing 16 bytes into a region of size 0 [-Werror=stringop-overflow=]
 1072 |             ((unsigned char*)hmac->innerHash)[j] |= hashBlock[j] & isOutBlock;
      |             ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~
src/tls.c: In function ‘TLS_hmac’:
src/tls.c:1277:12: note: at offset 560 into destination object ‘hmac’ of size 560
 1277 |     Hmac   hmac;
      |            ^~~~

Testing

How did you test?

Checklist

• added tests
• updated/added doxygen
• updated appropriate READMEs
• Updated manual and documentation