fix mixing up of SDL and libc allocators, proper flushing of quad build buffers

src/rendering/twn_sprites.c

@@ -244,6 +244,8 @@ void render_sprite_batch(const Primitive2D primitives[],
 
             push_quad_payload_to_vertex_buffer_builder(batch, i, &payload, v0, v1, v2, v3, uv0, uv1, uv2, uv3, sprite.color);
         }
+
+        finish_vertex_builder(&payload);
     }
 
     finally_render_quads(primitives, batch, vertex_array);