[HOTFIX] Fixed error InvalidCastException in MySqlClient.Driver.LoadCharacterSet

[rostov114]

This error may occur when using the latest versions of MariaDB.

MySql handle raised an exception (InvalidCastException: Object cannot be cast from DBNull to other types.)
  at System.DBNull.System.IConvertible.ToInt32 (System.IFormatProvider provider) [0x00000] in <2161c9885dd04ff291b79db9349c4b9b>:0 
  at System.Convert.ToInt32 (System.Object value, System.IFormatProvider provider) [0x00003] in <2161c9885dd04ff291b79db9349c4b9b>:0 
  at MySql.Data.MySqlClient.Driver.LoadCharacterSets (MySql.Data.MySqlClient.MySqlConnection connection) [0x00079] in <8d7380b3d3cf4bd8be324c584f371b44>:0 
  at MySql.Data.MySqlClient.Driver.Configure (MySql.Data.MySqlClient.MySqlConnection connection) [0x00060] in <8d7380b3d3cf4bd8be324c584f371b44>:0 
  at MySql.Data.MySqlClient.MySqlConnection.Open () [0x00198] in <8d7380b3d3cf4bd8be324c584f371b44>:0 
  at Oxide.Core.MySql.Libraries.MySql+MySqlQuery.Handle () [0x00059] in <021a1dba6a754e42a6cc7771fdfee190>:0 

Due to the presence of charsets without Id

SHOW COLLATION result:

| uca1400_ai_ci                  | NULL     | NULL | NULL    | Yes      |       8 |
| uca1400_ai_cs                  | NULL     | NULL | NULL    | Yes      |       8 |
| uca1400_as_ci                  | NULL     | NULL | NULL    | Yes      |       8 |
| uca1400_as_cs                  | NULL     | NULL | NULL    | Yes      |       8 |
| uca1400_nopad_ai_ci            | NULL     | NULL | NULL    | Yes      |       8 |
...

Add condition in Driver.LoadCharacterSet over DnSpy

if (mySqlDataReader["id"] != DBNull.Value)
{
	this.charSets[Convert.ToInt32(mySqlDataReader["id"], NumberFormatInfo.InvariantInfo)] = mySqlDataReader.GetString(mySqlDataReader.GetOrdinal("charset"));
}