ec_kmgmt.c: Do not crash when getting OSSL_PKEY_PARAM_ENCODED_PUBLIC_KEY

If the public key is not set on the key, return error instead of crash.

Fixes #18495

Reviewed-by: Paul Dale <pauli@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from #18902)

(cherry picked from commit b5db237)

providers/implementations/keymgmt/ec_kmgmt.c

@@ -637,8 +637,10 @@ int common_get_params(void *key, OSSL_PARAM params[], int sm2)
     BN_CTX *bnctx = NULL;
 
     ecg = EC_KEY_get0_group(eck);
-    if (ecg == NULL)
+    if (ecg == NULL) {
+        ERR_raise(ERR_LIB_PROV, PROV_R_NO_PARAMETERS_SET);
         return 0;
+    }
 
     libctx = ossl_ec_key_get_libctx(eck);
     propq = ossl_ec_key_get0_propq(eck);
@@ -727,8 +729,13 @@ int common_get_params(void *key, OSSL_PARAM params[], int sm2)
     }
     if ((p = OSSL_PARAM_locate(params,
                                OSSL_PKEY_PARAM_ENCODED_PUBLIC_KEY)) != NULL) {
-        p->return_size = EC_POINT_point2oct(EC_KEY_get0_group(key),
-                                            EC_KEY_get0_public_key(key),
+        const EC_POINT *ecp = EC_KEY_get0_public_key(key);
+
+        if (ecp == NULL) {
+            ERR_raise(ERR_LIB_PROV, PROV_R_NOT_A_PUBLIC_KEY);
+            goto err;
+        }
+        p->return_size = EC_POINT_point2oct(ecg, ecp,
                                             POINT_CONVERSION_UNCOMPRESSED,
                                             p->data, p->return_size, bnctx);
         if (p->return_size == 0)