error when tmysql4 is preferred but not installed

[Aws0mee]

When tmysql4 is the preferred module, but it is not installed an error will be thrown which will prevent the rest of the code in the file from running and will break the gamemode.

[ERROR] gamemodes/darkrp/gamemode/libraries/mysqlite/mysqlite.lua:143: attempt to index global 'tmysql' (a nil value)
  1. loadMySQLModule - gamemodes/darkrp/gamemode/libraries/mysqlite/mysqlite.lua:143
   2. unknown - gamemodes/darkrp/gamemode/libraries/mysqlite/mysqlite.lua:153
    3. include - [C]:-1
     4. unknown - gamemodes/darkrp/gamemode/init.lua:42