SDL_GetMouseNameForID(): Set an error message for invalid mouse IDs.

[Sackzement]

Currently SDL_GetMouseNameForID() doesn't set an error message, when passing an invalid mouse ID:

if(!SDL_GetMouseNameForID(99)) {
    printf("Error \"%s\"", SDL_GetError());
}

Prints

""

This commits sets an error message when the function fails.

The style of the message is inspired by a similar joystick error message:

SDL/src/joystick/SDL_joystick.c

Line 515 in 68cc173

SDL_SetError("Joystick %" SDL_PRIu32 " not found", instance_id);