Don't run SDL_IterateMainCallbacks() if the init call returns an exit code

This fixes a crash in testsprite if you pass invalid command line parameters.

src/main/generic/SDL_sysmain_callbacks.c

@@ -38,41 +38,41 @@ static void SDLCALL MainCallbackRateHintChanged(void *userdata, const char *name
 int SDL_EnterAppMainCallbacks(int argc, char* argv[], SDL_AppInit_func appinit, SDL_AppIterate_func appiter, SDL_AppEvent_func appevent, SDL_AppQuit_func appquit)
 {
     int rc = SDL_InitMainCallbacks(argc, argv, appinit, appiter, appevent, appquit);
+    if (rc == 0) {
+        SDL_AddHintCallback(SDL_HINT_MAIN_CALLBACK_RATE, MainCallbackRateHintChanged, NULL);
 
-    SDL_AddHintCallback(SDL_HINT_MAIN_CALLBACK_RATE, MainCallbackRateHintChanged, NULL);
+        Uint64 next_iteration = callback_rate_increment ? (SDL_GetTicksNS() + callback_rate_increment) : 0;
 
-    Uint64 next_iteration = callback_rate_increment ? (SDL_GetTicksNS() + callback_rate_increment) : 0;
+        while ((rc = SDL_IterateMainCallbacks()) == 0) {
+            // !!! FIXME: this can be made more complicated if we decide to
+            // !!! FIXME: optionally hand off callback responsibility to the
+            // !!! FIXME: video subsystem (for example, if Wayland has a
+            // !!! FIXME: protocol to drive an animation loop, maybe we hand
+            // !!! FIXME: off to them here if/when the video subsystem becomes
+            // !!! FIXME: initialized).
 
-    while ((rc = SDL_IterateMainCallbacks()) == 0) {
-        // !!! FIXME: this can be made more complicated if we decide to
-        // !!! FIXME: optionally hand off callback responsibility to the
-        // !!! FIXME: video subsystem (for example, if Wayland has a
-        // !!! FIXME: protocol to drive an animation loop, maybe we hand
-        // !!! FIXME: off to them here if/when the video subsystem becomes
-        // !!! FIXME: initialized).
-
-        // !!! FIXME: maybe respect this hint even if there _is_ a window.
-        // if there's no window, try to run at about 60fps (or whatever rate
-        //  the hint requested). This makes this not eat all the CPU in
-        //  simple things like loopwave. If there's a window, we run as fast
-        //  as possible, which means we'll clamp to vsync in common cases,
-        //  and won't be restrained to vsync if the app is doing a benchmark
-        //  or doesn't want to be, based on how they've set up that window.
-        if ((callback_rate_increment == 0) || SDL_HasWindows()) {
-            next_iteration = 0;  // just clear the timer and run at the pace the video subsystem allows.
-        } else {
-            const Uint64 now = SDL_GetTicksNS();
-            if (next_iteration > now) {  // Running faster than the limit, sleep a little.
-                SDL_DelayNS(next_iteration - now);
+            // !!! FIXME: maybe respect this hint even if there _is_ a window.
+            // if there's no window, try to run at about 60fps (or whatever rate
+            //  the hint requested). This makes this not eat all the CPU in
+            //  simple things like loopwave. If there's a window, we run as fast
+            //  as possible, which means we'll clamp to vsync in common cases,
+            //  and won't be restrained to vsync if the app is doing a benchmark
+            //  or doesn't want to be, based on how they've set up that window.
+            if ((callback_rate_increment == 0) || SDL_HasWindows()) {
+                next_iteration = 0; // just clear the timer and run at the pace the video subsystem allows.
             } else {
-                next_iteration = now;  // running behind (or just lost the window)...reset the timer.
+                const Uint64 now = SDL_GetTicksNS();
+                if (next_iteration > now) { // Running faster than the limit, sleep a little.
+                    SDL_DelayNS(next_iteration - now);
+                } else {
+                    next_iteration = now; // running behind (or just lost the window)...reset the timer.
+                }
+                next_iteration += callback_rate_increment;
             }
-            next_iteration += callback_rate_increment;
         }
-    }
-
-    SDL_DelHintCallback(SDL_HINT_MAIN_CALLBACK_RATE, MainCallbackRateHintChanged, NULL);
 
+        SDL_DelHintCallback(SDL_HINT_MAIN_CALLBACK_RATE, MainCallbackRateHintChanged, NULL);
+    }
     SDL_QuitMainCallbacks();
 
     return (rc < 0) ? 1 : 0;