Check if SDL_ttf is initialized.
Returns the current number of initialization calls, that need to eventually be paired with this many calls to TTF_Quit().
This reports the number of times the library has been initialized by a call to TTF_Init(), without a paired deinitialization request from TTF_Quit().
In short: if it's greater than zero, the library is currently initialized and ready to work. If zero, it is not initialized.
Despite the return value being a signed integer, this function should not return a negative number.