Fix Coverity warning about contrib/pgcrypto's mdc_finish().
Fix Coverity warning about contrib/pgcrypto's mdc_finish().

Coverity points out that mdc_finish returns a pointer to a local buffer
(which of course is gone as soon as the function returns), leaving open
a risk of misbehaviors possibly as bad as a stack overwrite.

In reality, the only possible call site is in process_data_packets()
which does not examine the returned pointer at all.  So there's no
live bug, but nonetheless the code is confusing and risky.  Refactor
to avoid the issue by letting process_data_packets() call mdc_finish()
directly instead of going through the pullf_read() API.

Although this is only cosmetic, it seems good to back-patch so that
the logic in pgp-decrypt.c stays in sync across all branches.

Marko Kreen

Chibin/gpdb,Quikling/gpdb,lisakowen/gpdb,cjcjameson/gpdb,edespino/gpdb,edespino/gpdb,greenplum-db/gpdb,janebeckman/gpdb,lisakowen/gpdb,50wu/gpdb,adam8157/gpdb,kaknikhil/gpdb,Chibin/gpdb,rvs/gpdb,50wu/gpdb,rvs/gpdb,janebeckman/gpdb,greenplum-db/gpdb,50wu/gpdb,jmcatamney/gpdb,lisakowen/gpdb,janebeckman/gpdb,xinzweb/gpdb,Chibin/gpdb,kaknikhil/gpdb,greenplum-db/gpdb,adam8157/gpdb,janebeckman/gpdb,edespino/gpdb,Quikling/gpdb,ashwinstar/gpdb,greenplum-db/gpdb,edespino/gpdb,Chibin/gpdb,lisakowen/gpdb,rvs/gpdb,yuanzhao/gpdb,ashwinstar/gpdb,cjcjameson/gpdb,jmcatamney/gpdb,lisakowen/gpdb,edespino/gpdb,Quikling/gpdb,yuanzhao/gpdb,Quikling/gpdb,xinzweb/gpdb,rvs/gpdb,Quikling/gpdb,adam8157/gpdb,janebeckman/gpdb,50wu/gpdb,kaknikhil/gpdb,Quikling/gpdb,adam8157/gpdb,Chibin/gpdb,jmcatamney/gpdb,yuanzhao/gpdb,cjcjameson/gpdb,edespino/gpdb,adam8157/gpdb,50wu/gpdb,edespino/gpdb,xinzweb/gpdb,xinzweb/gpdb,adam8157/gpdb,ashwinstar/gpdb,cjcjameson/gpdb,greenplum-db/gpdb,xinzweb/gpdb,jmcatamney/gpdb,edespino/gpdb,yuanzhao/gpdb,jmcatamney/gpdb,janebeckman/gpdb,ashwinstar/gpdb,Quikling/gpdb,kaknikhil/gpdb,janebeckman/gpdb,50wu/gpdb,ashwinstar/gpdb,greenplum-db/gpdb,yuanzhao/gpdb,cjcjameson/gpdb,cjcjameson/gpdb,yuanzhao/gpdb,ashwinstar/gpdb,xinzweb/gpdb,ashwinstar/gpdb,xinzweb/gpdb,kaknikhil/gpdb,50wu/gpdb,rvs/gpdb,rvs/gpdb,lisakowen/gpdb,ashwinstar/gpdb,cjcjameson/gpdb,janebeckman/gpdb,greenplum-db/gpdb,cjcjameson/gpdb,greenplum-db/gpdb,yuanzhao/gpdb,cjcjameson/gpdb,rvs/gpdb,Quikling/gpdb,lisakowen/gpdb,janebeckman/gpdb,Quikling/gpdb,yuanzhao/gpdb,50wu/gpdb,kaknikhil/gpdb,rvs/gpdb,Chibin/gpdb,xinzweb/gpdb,yuanzhao/gpdb,kaknikhil/gpdb,adam8157/gpdb,jmcatamney/gpdb,Chibin/gpdb,edespino/gpdb,Chibin/gpdb,janebeckman/gpdb,Chibin/gpdb,adam8157/gpdb,jmcatamney/gpdb,yuanzhao/gpdb,lisakowen/gpdb,edespino/gpdb,rvs/gpdb,rvs/gpdb,Chibin/gpdb,Quikling/gpdb,kaknikhil/gpdb,jmcatamney/gpdb,kaknikhil/gpdb,cjcjameson/gpdb,kaknikhil/gpdb