Clean up sloppy coding in publicationcmds.c's OpenTableList().

Remove dead code (which would be incorrect if it weren't dead),
per report from Pan Bian.  Add a CHECK_FOR_INTERRUPTS in the
inner loop over child relations, because there's little point
in having one in the outer loop if there's not one here too.
Minor stylistic adjustments and comment improvements.

Seems to be aboriginal to this code (cf commit 665d1fad).
Back-patch to v10 where that came in, not because any of this
is significant, but just to keep the branches looking similar.

Discussion: https://postgr.es/m/15539-06d00ef6b1e2e1bb@postgresql.org

src/backend/commands/publicationcmds.c

@@ -494,7 +494,7 @@ RemovePublicationRelById(Oid proid)
 }
 
 /*
- * Open relations based on provided by RangeVar list.
+ * Open relations specified by a RangeVar list.
  * The returned tables are locked in ShareUpdateExclusiveLock mode.
  */
 static List *
@@ -509,11 +509,12 @@ OpenTableList(List *tables)
 	 */
 	foreach(lc, tables)
 	{
-		RangeVar   *rv = lfirst(lc);
-		Relation	rel;
+		RangeVar   *rv = castNode(RangeVar, lfirst(lc));
 		bool		recurse = rv->inh;
+		Relation	rel;
 		Oid			myrelid;
 
+		/* Allow query cancel in case this takes a long time */
 		CHECK_FOR_INTERRUPTS();
 
 		rel = heap_openrv(rv, ShareUpdateExclusiveLock);
@@ -531,13 +532,15 @@ OpenTableList(List *tables)
 			heap_close(rel, ShareUpdateExclusiveLock);
 			continue;
 		}
+
 		rels = lappend(rels, rel);
 		relids = lappend_oid(relids, myrelid);
 
+		/* Add children of this rel, if requested */
 		if (recurse)
 		{
-			ListCell   *child;
 			List	   *children;
+			ListCell   *child;
 
 			children = find_all_inheritors(myrelid, ShareUpdateExclusiveLock,
 										   NULL);
@@ -546,18 +549,15 @@ OpenTableList(List *tables)
 			{
 				Oid			childrelid = lfirst_oid(child);
 
-				if (list_member_oid(relids, childrelid))
-					continue;
+				/* Allow query cancel in case this takes a long time */
+				CHECK_FOR_INTERRUPTS();
 
 				/*
 				 * Skip duplicates if user specified both parent and child
 				 * tables.
 				 */
 				if (list_member_oid(relids, childrelid))
-				{
-					heap_close(rel, ShareUpdateExclusiveLock);
 					continue;
-				}
 
 				/* find_all_inheritors already got lock */
 				rel = heap_open(childrelid, NoLock);