ecpg: Restore detection of unsupported COPY FROM STDIN.

The ecpg command includes code to warn about unsupported COPY FROM STDIN
statements in input files. However, since commit 3d009e4,
this functionality has been broken due to a bug introduced in that commit,
causing ecpg to fail to detect the statement.

This commit resolves the issue, restoring ecpg's ability to detect
COPY FROM STDIN and issue a warning as intended.

Back-patch to all supported versions.

Author: Ryo Kanbayashi
Reviewed-by: Hayato Kuroda, Tom Lane
Discussion: https://postgr.es/m/CANOn0Ez_t5uDCUEV8c1YORMisJiU5wu681eEVZzgKwOeiKhkqQ@mail.gmail.com

Author: MasaoFujii

src/interfaces/ecpg/preproc/ecpg.addons

@@ -240,7 +240,7 @@ ECPG: block where_or_current_clause WHERE CURRENT_P OF cursor_name
 		@$ = cat_str(2, "where current of", cursor_marker);
 	}
 ECPG: addon CopyStmt COPY opt_binary qualified_name opt_column_list copy_from opt_program copy_file_name copy_delimiter opt_with copy_options where_clause
-		if (strcmp(@6, "from") == 0 &&
+		if (strcmp(@5, "from") == 0 &&
 			(strcmp(@7, "stdin") == 0 || strcmp(@7, "stdout") == 0))
 			mmerror(PARSE_ERROR, ET_WARNING, "COPY FROM STDIN is not implemented");
 ECPG: addon var_value NumericOnly