mp_image: add missing field to mp_image_params_equals()

This is pretty obscure, so it didn't matter much. It still breaks
switching output levels at runtime, because the video output is not
reinitialized with the new params.

video/mp_image.c

@@ -439,6 +439,7 @@ bool mp_image_params_equals(const struct mp_image_params *p1,
            p1->d_w == p2->d_w && p1->d_h == p2->d_h &&
            p1->colorspace == p2->colorspace &&
            p1->colorlevels == p2->colorlevels &&
+           p1->outputlevels == p2->outputlevels &&
            p1->chroma_location == p2->chroma_location;
 }