[mysql] close connection causes segfault

Using `MysqlConnection.close()` causes segfault using either hashlink virtual machine or native c code.

Using `HL/JIT 1.11.0`
And Mysql: `mysql Ver 15.1 Distrib 10.5.5-MariaDB, for Linux (x86_64) using readline 5.1`
Outputs:
**HL Virtual Machine**
```
SIGNAL 11
sys.db._Mysql.MysqlConnection.close(/usr/share/haxe/std/hl/_std/sys/db/Mysql.hx:140)
$Server.main(Server.hx:12)
fun$430(?:1)
@0x5A4E9310
zsh: segmentation fault (core dumped)
```
**Native C Compile**
```
zsh: segmentation fault (core dumped) ./a.out
```

Problem is caused exactly in `close_wrap` function in `mysql.c`: `mp_close(c->c)`

Unsure if it's mysql bug or hashlink.