In load_relcache_init_file, initialize rd_pdcxt.

Oversight noted by Gao Zeng Qi.

Discussion: http://postgr.es/m/CAFmBtr1N3-SbepJbnGpaYp=jw-FvWMnYY7-bTtRgvjvbyB8YJA@mail.gmail.com

src/backend/utils/cache/relcache.c

@@ -5608,6 +5608,7 @@ load_relcache_init_file(bool shared)
 		rel->rd_rsdesc = NULL;
 		rel->rd_partkeycxt = NULL;
 		rel->rd_partkey = NULL;
+		rel->rd_pdcxt = NULL;
 		rel->rd_partdesc = NULL;
 		rel->rd_partcheck = NIL;
 		rel->rd_indexprs = NIL;