Fix segfault when rendering fonts

docs/reST/ref/font.rst

@@ -57,6 +57,8 @@ solves no longer exists, it will likely be removed in the future.
 
    It is safe to call this function even if font is currently not initialized.
 
+   Previously created font objects will be invalid after the font module is quit.
+
    .. ## pygame.font.quit ##
 
 .. function:: get_init

src_c/font.c

@@ -61,6 +61,10 @@ PyFont_New(TTF_Font *);
 #define PyFont_Check(x) ((x)->ob_type == &PyFont_Type)
 
 static unsigned int current_ttf_generation = 0;
+
+#define PgFont_GenerationCheck(x) \
+    (((PyFontObject *)(x))->ttf_init_generation == current_ttf_generation)
+
 #if defined(BUILD_STATIC)
 // SDL_Init + TTF_Init()  are made in main before CPython process the module
 // inittab so the emscripten handler knows it will use SDL2 next cycle.
@@ -486,6 +490,11 @@ font_render(PyObject *self, PyObject *args, PyObject *kwds)
     const char *astring = "";
     int wraplength = 0;
 
+    if (!PgFont_GenerationCheck(self)) {
+        return RAISE(pgExc_SDLError,
+                     "Invalid font (font module quit since font created)");
+    }
+
     static char *kwlist[] = {"text",    "antialias",  "color",
                              "bgcolor", "wraplength", NULL};
 
@@ -610,6 +619,11 @@ font_size(PyObject *self, PyObject *text)
     int w, h;
     const char *string;
 
+    if (!PgFont_GenerationCheck(self)) {
+        return RAISE(pgExc_SDLError,
+                     "Invalid font (font module quit since font created)");
+    }
+
     if (PyUnicode_Check(text)) {
         PyObject *bytes = PyUnicode_AsEncodedString(text, "utf-8", "strict");
         int ecode;
@@ -664,6 +678,11 @@ font_metrics(PyObject *self, PyObject *textobj)
     PyObject *temp;
     int surrogate;
 
+    if (!PgFont_GenerationCheck(self)) {
+        return RAISE(pgExc_SDLError,
+                     "Invalid font (font module quit since font created)");
+    }
+
     if (PyUnicode_Check(textobj)) {
         obj = textobj;
         Py_INCREF(obj);