pg_stat_statements: Fix normalization of + signs for FETCH and MOVE

Hi,

While revisiting feature “Show sizes of FETCH queries as constants in pg_stat_statements”, I found another issue where “+” is not properly handled.

See this repro:
```
evantest=*# fetch + 1 c;
g
---
(0 rows)

evantest=*# select calls, query from pg_stat_statements where query like 'fetch%';
calls | query
-------+--------------
1 | fetch $1 1 c
(1 row)

evantest=*# SELECT pg_stat_statements_reset();
pg_stat_statements_reset
-------------------------------
2026-06-01 08:59:19.538839+08
(1 row)

evantest=*# fetch +1 c;
g
---
(0 rows)

evantest=*# select calls, query from pg_stat_statements where query like 'fetch%';
calls | query
-------+-------------
1 | fetch $11 c
(1 row)
```

As shown above, the "+" sign is replaced separately from the integer. However, a "-" sign is handled correctly:
```
evantest=*# SELECT pg_stat_statements_reset();
pg_stat_statements_reset
-------------------------------
2026-06-01 09:09:48.776385+08
(1 row)

evantest=*# fetch - 1 c;
g
----
10
(1 row)

evantest=*# select calls, query from pg_stat_statements where query like 'fetch%';
calls | query
-------+------------
1 | fetch $1 c
(1 row)
```

The same issue exists for “MOVE” as well:
```
evantest=*# move relative + 2 c;
MOVE 0
evantest=*# select calls, query from pg_stat_statements where query like 'move%';
calls | query
-------+----------------------
1 | move relative $1 2 c
(1 row)
```

The fix seems simple, as the "-" sign is already handled:
```
/*
* We should find the token position exactly, but if we somehow
* run past it, work with that.
*/
if (yylloc >= loc)
{
if (query[loc] == '-')
{
/*
* It's a negative value - this is the one and only case
* where we replace more than a single token.
*
* Do not compensate for the special-case adjustment of
* location to that of the leading '-' operator in the
* event of a negative constant (see doNegate() in
* gram.y). It is also useful for our purposes to start
* from the minus symbol. In this way, queries like
* "select * from foo where bar = 1" and "select * from
* foo where bar = -2" can be treated similarly.
*/
```

We just need to handle "+" in the same way. See the attached patch for details.

Best regards,
--
Chao Li (Evan)
HighGo Software Co., Ltd.
https://www.highgo.com/