Fix some return checks in ecdh_cms_encrypt()

Fix some return checks in ecdh_cms_encrypt()

i2d functions return <= 0 on error, so check for that instead of == 0.

The issue with CMS_SharedInfo_encode() was found by Niels Dossche.
OpenSSL review overlooked that they had turned penclen into a size_t.

In principle the issue with i2d_X509_ALGOR() is purely cosmetic. Why do
a strange check when there is an idiomatic check? Then again this is CMS...

ok jsing