Replace isString() with isCString() in both the global-variable and
struct-field encoding paths. isString() matches any [N x i8] array,
including binary data arrays (bitmasks, protocol constants, numeric
byte tables) that happen to have no embedded null bytes. isCString()
restricts encryption to proper null-terminated C strings only.
This prevents the pass from encrypting arrays like QUIC crypto labels,
DTLS bitmask tables, and test data arrays such as {1,1,...,1}, which
caused memory corruption and test failures in the OpenSSL QUIC ACK
manager test (75-test_quic_ackm.t).
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Patrice Blin