pgsql: Fixed remaining Coverity bugs.

Log Message:
-----------
Fixed remaining Coverity bugs.

Modified Files:
--------------
    pgsql/src/interfaces/ecpg:
        ChangeLog (r1.310 -> r1.311)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/ecpg/ChangeLog.diff?r1=1.310&r2=1.311)
    pgsql/src/interfaces/ecpg/ecpglib:
        descriptor.c (r1.16 -> r1.17)

(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/ecpg/ecpglib/descriptor.c.diff?r1=1.16&r2=1.17)
        execute.c (r1.50 -> r1.51)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/ecpg/ecpglib/execute.c.diff?r1=1.50&r2=1.51)