Use "#ifdef CATALOG_VARLEN" to protect nullable fields of pg_authid.

This gives a stronger guarantee than a mere comment against accessing these
fields as simple struct members.  Since rolpassword is in fact varlena,
it's not clear why these didn't get marked from the beginning, but let's
do it now.

Michael Paquier

src/include/catalog/pg_authid.h

@@ -56,8 +56,10 @@ CATALOG(pg_authid,1260) BKI_SHARED_RELATION BKI_ROWTYPE_OID(2842) BKI_SCHEMA_MAC
 	int32		rolconnlimit;	/* max connections allowed (-1=no limit) */
 
 	/* remaining fields may be null; use heap_getattr to read them! */
+#ifdef CATALOG_VARLEN			/* variable-length fields start here */
 	text		rolpassword;	/* password, if any */
 	timestamptz rolvaliduntil;	/* password expiration time, if any */
+#endif
 } FormData_pg_authid;
 
 #undef timestamptz