[PGPRO-11393] Fixed the content of the error message

If the "RUM" index was created without the "WITH" operator,
when "SELECT...ORDER BY" an error message of the form would appear:

  "ERROR: cannot order without attribute ... in WHERE clause"

Fixed the content of error message, "WHERE" replaced by "ORDER BY".

Tags: rum

Author: arseny114

src/rumscan.c

@@ -214,7 +214,7 @@ rumFillScanKey(RumScanOpaque so, OffsetNumber attnum,
 				}
 
 				if (scanKey == NULL)
-					elog(ERROR, "cannot order without attribute %d in WHERE clause",
+					elog(ERROR, "cannot order without attribute %d in ORDER BY clause",
 						 key->attnum);
 				else if (scanKey->nentries > 1)
 					elog(ERROR, "scan key should contain only one value");