sub: unprefer libavcodec's MicroDVD converter

Prefer the builtin one again. libavcodec still uses the ASS packet
format that uses inline timestamps, so the packet timestamps are
ignored. This again leads to additional rounding of timestamps, because
the ASS storage format only has 10ms resolution (instead of 1ms
resolution like libass). This again can lead to unintentional overlaps
when converting subtitles. The internal MicroDVD converter avoids this,
because it always uses packet timestamps.

sub/dec_sub.c

@@ -49,8 +49,8 @@ static const struct sd_functions *const sd_list[] = {
     &sd_movtext,
     &sd_srt,
     &sd_lavf_srt,
-    &sd_lavc_conv,
     &sd_microdvd,
+    &sd_lavc_conv,
     NULL
 };