Fix segfault when rendering fonts

[yunline]

Fixes: #1506
Test code:

import pygame

pygame.init()
font = pygame.font.Font(None, 40)

pygame.quit()
pygame.init()

font.render("hello", True, "white")
#font.size("hello")
#font.metrics("hello")

Now it will raise an error instead of segfault

pygame-ce 2.3.1.dev1 (SDL 2.26.4, Python 3.10.6)
Traceback (most recent call last):
  File "x:\python\pygame_test\segfault.py", line 10, in <module>
    font.render("hello", True, "white")
pygame.error: Invalid font.

[andrewhong04]

I see nothing out of the ordinary. LGTM!

[Starbuck5]

This looks great!

I'm wondering if we can be more clear with the "invalid font" error message. "Invalid font (font module quit since font created)" ?

It would also be good to add some documentation about this whole generation constraint. I think it would go well as another line in pygame.font.quit, mentioning that previously created font objects become invalid after the font module is quit.

[Starbuck5]

Thanks!