Fix buffer overflow in writeHashEntry()
Fix buffer overflow in writeHashEntry()

MAXALIGN(datum_size) can be greater than BUFFER_INCREMENT_SIZE, hence
when allocating the buffer need to make sure buffer has enough space
for writing the next datum.

ashwinstar/gpdb,50wu/gpdb,ashwinstar/gpdb,lisakowen/gpdb,lisakowen/gpdb,greenplum-db/gpdb,adam8157/gpdb,lisakowen/gpdb,50wu/gpdb,adam8157/gpdb,ashwinstar/gpdb,xinzweb/gpdb,greenplum-db/gpdb,xinzweb/gpdb,xinzweb/gpdb,ashwinstar/gpdb,lisakowen/gpdb,lisakowen/gpdb,ashwinstar/gpdb,xinzweb/gpdb,adam8157/gpdb,xinzweb/gpdb,jmcatamney/gpdb,greenplum-db/gpdb,ashwinstar/gpdb,xinzweb/gpdb,lisakowen/gpdb,50wu/gpdb,greenplum-db/gpdb,greenplum-db/gpdb,adam8157/gpdb,50wu/gpdb,greenplum-db/gpdb,greenplum-db/gpdb,xinzweb/gpdb,jmcatamney/gpdb,xinzweb/gpdb,50wu/gpdb,50wu/gpdb,jmcatamney/gpdb,lisakowen/gpdb,adam8157/gpdb,ashwinstar/gpdb,adam8157/gpdb,50wu/gpdb,adam8157/gpdb,ashwinstar/gpdb,50wu/gpdb,jmcatamney/gpdb,jmcatamney/gpdb,jmcatamney/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,lisakowen/gpdb,jmcatamney/gpdb,adam8157/gpdb