Revert "vd_lavc: do not abort hardware decoding on errors"

This essentially reverts commit 009dfbe3. FFmpeg VideoToolbox support
is being wacky, and can cause major issues, such as not being able
to decode a single frame. (E.g. by playing a .ts file. This should be
fixed in FFmpeg eventually.)

This is not a straight revert of the commit; just a functional one. We
keep the slightly simpler code structure.

video/decode/vd_lavc.c

@@ -627,6 +627,7 @@ static void decode(struct dec_video *vd, struct demux_packet *packet,
     if (ctx->hwdec_failed || ret < 0) {
         if (ret < 0)
             MP_WARN(vd, "Error while decoding frame!\n");
+        ctx->hwdec_failed = true;
         return;
     }