Re-add SDL_assert() with non boolean ptr syntax (#8531)

src/haptic/android/SDL_syshaptic.c

@@ -70,7 +70,7 @@ static SDL_hapticlist_item *HapticByOrder(int index)
         return NULL;
     }
     while (index > 0) {
-        SDL_assert(item);
+        SDL_assert(item != NULL);
         --index;
         item = item->next;
     }

src/haptic/darwin/SDL_syshaptic.c

@@ -196,7 +196,7 @@ static SDL_hapticlist_item *HapticByDevIndex(int device_index)
     }
 
     while (device_index > 0) {
-        SDL_assert(item);
+        SDL_assert(item != NULL);
         --device_index;
         item = item->next;
     }

src/haptic/linux/SDL_syshaptic.c

@@ -195,7 +195,7 @@ static SDL_hapticlist_item *HapticByDevIndex(int device_index)
     }
 
     while (device_index > 0) {
-        SDL_assert(item);
+        SDL_assert(item != NULL);
         --device_index;
         item = item->next;
     }

src/haptic/windows/SDL_windowshaptic.c

@@ -126,7 +126,7 @@ static SDL_hapticlist_item *HapticByDevIndex(int device_index)
     }
 
     while (device_index > 0) {
-        SDL_assert(item);
+        SDL_assert(item != NULL);
         --device_index;
         item = item->next;
     }