Also document CMS_decrypt_set1_password() and fix CMS_EnvelopedData_create.pod.

…ecryption key

…ent mismatch was not the issue

Fixes openssl#19975
for CMS_decrypt_set1_pkey_and_peer() in the obvious way,
and a related potential crash in CMS_decrypt_set1_password().

The point is that the input might have an unexpected content type,
so a guard is needed at both places after `ec` is obtained.

Note that in CMS_decrypt_set1_pkey_and_peer() there was
no such ec != NULL guard for
```
    if (ris != NULL)
        debug = ec->debug;
```
maybe because it is implied here by ris != NULL.