pgsql-server: Defend against overrun of ExtraOptions array --- strictly

Log Message:
-----------
Defend against overrun of ExtraOptions array --- strictly paranoia,
since the person or script starting the postmaster has to be trusted
anyway.

Modified Files:
--------------
pgsql-server/src/backend/postmaster:
postmaster.c (r1.405 -> r1.406)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/postmaster/postmaster.c.diff?r1=1.405&r2=1.406)