srtpkdf.c: avoid ctx NULL dereference kdf_srtpkdf_set_ctx_params()

srtpkdf.c: avoid ctx NULL dereference kdf_srtpkdf_set_ctx_params()

ctx is dereferenced before NULL check to obtain libctx.  Fix it
by moving the dereference after the NULL check.

Resolves: https://scan5.scan.coverity.com/#/project-view/65248/10222?selectedIssue=1680648
Fixes: fe67753da4096 "Add SRTPKDF implementation"
Signed-off-by: Eugene Syromiatnikov <esyr@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Paul Dale <paul.dale@oracle.com>
Reviewed-by: Norbert Pocs <norbertp@openssl.org>
Reviewed-by: Shane Lontis <shane.lontis@oracle.com>
Reviewed-by: Neil Horman <nhorman@openssl.org>
MergeDate: Wed Jan 28 12:57:00 2026
(Merged from https://github.com/openssl/openssl/pull/29757)