cms: fix coverity 1485981: unchecked return value

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: David von Oheimb <david.von.oheimb@siemens.com>
(Merged from https://github.com/openssl/openssl/pull/15731)

crypto/cms/cms_ec.c

@@ -20,12 +20,12 @@ static EVP_PKEY *pkey_type2param(int ptype, const void *pval,
 {
     EVP_PKEY *pkey = NULL;
     EVP_PKEY_CTX *pctx = NULL;
+    OSSL_DECODER_CTX *ctx = NULL;
 
     if (ptype == V_ASN1_SEQUENCE) {
         const ASN1_STRING *pstr = pval;
         const unsigned char *pm = pstr->data;
         size_t pmlen = (size_t)pstr->length;
-        OSSL_DECODER_CTX *ctx = NULL;
         int selection = OSSL_KEYMGMT_SELECT_ALL_PARAMETERS;
 
         ctx = OSSL_DECODER_CTX_new_for_pkey(&pkey, "DER", NULL, "EC",
@@ -33,7 +33,10 @@ static EVP_PKEY *pkey_type2param(int ptype, const void *pval,
         if (ctx == NULL)
             goto err;
 
-        OSSL_DECODER_from_data(ctx, &pm, &pmlen);
+        if (!OSSL_DECODER_from_data(ctx, &pm, &pmlen)) {
+            ERR_raise(ERR_LIB_CMS, CMS_R_DECODE_ERROR);
+            goto err;
+        }    
         OSSL_DECODER_CTX_free(ctx);
     } else if (ptype == V_ASN1_OBJECT) {
         const ASN1_OBJECT *poid = pval;
@@ -60,6 +63,7 @@ static EVP_PKEY *pkey_type2param(int ptype, const void *pval,
  err:
     EVP_PKEY_free(pkey);
     EVP_PKEY_CTX_free(pctx);
+    OSSL_DECODER_CTX_free(ctx);
     return NULL;
 }