Dept of second thoughts: keep aliasp_item in sync with tlistitem.

Commit d5b760ec wasn't quite right, on second thought: if the
caller didn't ask for column names then it would happily emit
more Vars than if the caller did ask for column names.  This
is surely not a good idea.  Advance the aliasp_item whether or
not we're preparing a colnames list.

src/backend/parser/parse_relation.c

@@ -2221,7 +2221,6 @@ expandRTE(RangeTblEntry *rte, int rtindex, int sublevels_up,
 						char	   *label = strVal(lfirst(aliasp_item));
 
 						*colnames = lappend(*colnames, makeString(pstrdup(label)));
-						aliasp_item = lnext(aliasp_item);
 					}
 
 					if (colvars)
@@ -2237,6 +2236,8 @@ expandRTE(RangeTblEntry *rte, int rtindex, int sublevels_up,
 
 						*colvars = lappend(*colvars, varnode);
 					}
+
+					aliasp_item = lnext(aliasp_item);
 				}
 			}
 			break;