vd_lavc: don't request native pixfmt with -copy and METHOD_INTERNAL

If the codec uses AV_CODEC_HW_CONFIG_METHOD_INTERNAL, and we're using
the -copy method, then don't request the native pix_fmt. It might not
have a AVFrame.hw_frames_ctx set, and we couldn't read back at all. On
top of that, most of those decoders probably don't provide read-back
when using such opaque formats anyway, while providing separate decoding
modes to decode to RAM.

video/decode/vd_lavc.c

@@ -352,6 +352,7 @@ static void add_all_hwdec_methods(struct hwdec_info **infos, int *num_infos)
 
                 // Copy variant.
                 info.copying = true;
+                info.pix_fmt = AV_PIX_FMT_NONE; // trust it can do sw output
                 add_hwdec_item(infos, num_infos, info);
 
                 found_any = true;