[PATCH] Patch to fix a crash of psql

hi

When i test psql under multi-lingual and different encoding environment,
I found a crash of psql.

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$ export PGCLIENTENCODING=SJIS
$ psql
psql (9.2rc1)
Type "help" for help.

postgres=# \i sql
CREATE DATABASE
You are now connected to database "mydb" as user "postgres".
CREATE SCHEMA
Segmentation fault (core dumped)
$
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I'm look into this problem and found that
only some especial character can cause psql crash.
conditions is:
1. some especial character
(my sql file contains japanese comment "-- コメント" . It can cause
psql crash.)
2. PGCLIENTENCODING is SJIS
3. the encoding of input sql file is UTF-8

I investigated this problem. The reasons are as follows.
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src/bin/psql/mainloop.c
-> psql_scan_setup() //Set up to perform lexing of the given input line.
-->prepare_buffer () //Set up a flex input buffer to scan the given data.
---->malloc character buffer.
---->set two \0 characters. (Flex wants two \0 characters after the
actual data.)
---->working in an unsafe encoding, the copy has multibyte sequences
replaced by FFs to avoid fooling the lexer rules.
****the encoding of input sql file is different from PGCLIENTENCODING, two
\0 characters are replaced by FFs. ****

---->yy_scan_buffer() //Setup the input buffer state to scan directly
from a user-specified character buffer.
****because two \0 characters are replaced by FFs,yy_scan_buffer() return
0. input buffer state can not setup correctly.****

-> psql_scan() //Do lexical analysis of SQL command text.
--> yylex() //The main scanner function which does all the work.
****because input buffer state is not setup,so when access the input
buffer state,segmentation fault is happened.****
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I modify src/bin/psql/psqlscan.l to resolve this problem.
The diff file refer to the attachment "psqlscan.l.patch".

Regards,
Jiang Guiqing