CheckNNConstraintFetch: Fill all of ConstrCheck in a single pass

Previously, we'd fill all fields except ccbin, and only later obtain and
detoast ccbin, with hypothetical failures being possible.  If ccbin is
null (rare catalog corruption I have never witnessed) or its a corrupted
toast entry, we leak a tiny bit of memory in CacheMemoryContext from
having strdup'd the constraint name.  Repair these by only attempting to
fill the struct once ccbin has been detoasted.

Author: Ranier Vilela <ranier.vf@gmail.com>
Discussion: https://postgr.es/m/CAEudQAr=i3_Z4GvmediX900+sSySTeMkvuytYShhQqEwoGyvhA@mail.gmail.com

src/backend/utils/cache/relcache.c

@@ -4658,12 +4658,6 @@ CheckNNConstraintFetch(Relation relation)
 			break;
 		}
 
-		check[found].ccenforced = conform->conenforced;
-		check[found].ccvalid = conform->convalidated;
-		check[found].ccnoinherit = conform->connoinherit;
-		check[found].ccname = MemoryContextStrdup(CacheMemoryContext,
-												  NameStr(conform->conname));
-
 		/* Grab and test conbin is actually set */
 		val = fastgetattr(htup,
 						  Anum_pg_constraint_conbin,
@@ -4676,7 +4670,13 @@ CheckNNConstraintFetch(Relation relation)
 			/* detoast and convert to cstring in caller's context */
 			char	   *s = TextDatumGetCString(val);
 
+			check[found].ccenforced = conform->conenforced;
+			check[found].ccvalid = conform->convalidated;
+			check[found].ccnoinherit = conform->connoinherit;
+			check[found].ccname = MemoryContextStrdup(CacheMemoryContext,
+													  NameStr(conform->conname));
 			check[found].ccbin = MemoryContextStrdup(CacheMemoryContext, s);
+
 			pfree(s);
 			found++;
 		}