Initialize key pointer in ecdh to NULL

Since it is being dereferenced by free on exit it should be inited to NULL.
Also added a small test that would trigger the issue.

Signed-off-by: Steven Cooreman <steven.cooreman@silabs.com>
diff --git a/library/psa_crypto.c b/library/psa_crypto.c
index d931a50..bc1619c 100644
--- a/library/psa_crypto.c
+++ b/library/psa_crypto.c
@@ -5586,7 +5586,7 @@
                                             size_t shared_secret_size,
                                             size_t *shared_secret_length )
 {
-    mbedtls_ecp_keypair *their_key;
+    mbedtls_ecp_keypair *their_key = NULL;
     mbedtls_ecdh_context ecdh;
     psa_status_t status;
     size_t bits = 0;
diff --git a/tests/suites/test_suite_psa_crypto.data b/tests/suites/test_suite_psa_crypto.data
index d1855fd..d982f81 100644
--- a/tests/suites/test_suite_psa_crypto.data
+++ b/tests/suites/test_suite_psa_crypto.data
@@ -2413,6 +2413,10 @@
 depends_on:MBEDTLS_PK_PARSE_C:MBEDTLS_ECP_C:MBEDTLS_ECP_DP_SECP256R1_ENABLED:MBEDTLS_ECDH_C:MBEDTLS_SHA256_C
 key_agreement_setup:PSA_ALG_KEY_AGREEMENT(PSA_ALG_ECDH, PSA_ALG_HKDF(PSA_ALG_SHA_256)):PSA_KEY_TYPE_ECC_KEY_PAIR(PSA_ECC_FAMILY_SECP_R1):"c88f01f510d9ac3f70a292daa2316de544e9aab8afe84049c62a9c57862d1433":"04d12dfb5289c8d4f81208b70270398c342296970a0bccb74c736fc7554494bf6356fbf3ca366cc23e8157854c13c58d6aac23f046ada30f8353e74f33039872ab":PSA_SUCCESS
 
+PSA key agreement setup: ECDH + HKDF-SHA-256: public key not on curve
+depends_on:MBEDTLS_PK_PARSE_C:MBEDTLS_ECP_C:MBEDTLS_ECP_DP_SECP256R1_ENABLED:MBEDTLS_ECDH_C:MBEDTLS_SHA256_C
+key_agreement_setup:PSA_ALG_KEY_AGREEMENT(PSA_ALG_ECDH, PSA_ALG_HKDF(PSA_ALG_SHA_256)):PSA_KEY_TYPE_ECC_KEY_PAIR(PSA_ECC_FAMILY_SECP_R1):"c88f01f510d9ac3f70a292daa2316de544e9aab8afe84049c62a9c57862d1433":"04d12dfb5289c8d4f81208b70270398c342296970a0bccb74c736fc7554494bf6356fbf3ca366cc23e8157854c13c58d6aac23f046ada30f8353e74f33039872ff":PSA_ERROR_INVALID_ARGUMENT
+
 PSA key agreement setup: ECDH + HKDF-SHA-256: public key on different curve
 depends_on:MBEDTLS_PK_PARSE_C:MBEDTLS_ECP_C:MBEDTLS_ECP_DP_SECP256R1_ENABLED:MBEDTLS_ECP_DP_SECP384R1_ENABLED:MBEDTLS_ECDH_C:MBEDTLS_SHA256_C
 key_agreement_setup:PSA_ALG_KEY_AGREEMENT(PSA_ALG_ECDH, PSA_ALG_HKDF(PSA_ALG_SHA_256)):PSA_KEY_TYPE_ECC_KEY_PAIR(PSA_ECC_FAMILY_SECP_R1):"c88f01f510d9ac3f70a292daa2316de544e9aab8afe84049c62a9c57862d1433":"04e558dbef53eecde3d3fccfc1aea08a89a987475d12fd950d83cfa41732bc509d0d1ac43a0336def96fda41d0774a3571dcfbec7aacf3196472169e838430367f66eebe3c6e70c416dd5f0c68759dd1fff83fa40142209dff5eaad96db9e6386c":PSA_ERROR_INVALID_ARGUMENT