ad_lavc: fix --ad-lavc-threads range

The code is shared with the --vd-lavc-threads option, so using 0 for
auto-detection just works.

But no, this is not useful. Just change it for orthogonality.

audio/decode/ad_lavc.c

@@ -59,7 +59,7 @@ const struct m_sub_options ad_lavc_conf = {
     .opts = (const m_option_t[]) {
         OPT_FLOATRANGE("ac3drc", ac3drc, 0, 0, 6),
         OPT_FLAG("downmix", downmix, 0),
-        OPT_INTRANGE("threads", threads, 0, 1, 16),
+        OPT_INTRANGE("threads", threads, 0, 0, 16),
         OPT_KEYVALUELIST("o", avopts, 0),
         {0}
     },