Fix bugs in --split-dvb-subs implementation

- Fix buffer offset: skip 2-byte header in multi-stream DVB path
- Fix Rust build: use ts_cappids.is_empty() instead of nb_ts_cappid
- Fix dangling pointer: set cfg to NULL after values are copied

Author: Rahul-2k4

src/lib_ccx/dvb_subtitle_decoder.c

@@ -582,7 +582,7 @@ struct ccx_decoders_dvb_context *dvb_init_decoder(struct dvb_config *cfg, int in
 	}
 
 	dvb_ctx->private_data = ctx;
-	dvb_ctx->cfg = cfg;
+	dvb_ctx->cfg = NULL;  // Config values are copied into DVBSubContext, don't store pointer
 	dvb_ctx->initialized_ocr = initialized_ocr;
 
 	return dvb_ctx;

src/lib_ccx/lib_ccx.c

@@ -561,7 +561,8 @@ int process_dvb_multi_stream(struct lib_ccx_ctx *ctx, struct demuxer_data *data,
 		return -1;
 	}
 
-	return route_dvb_stream_to_decoder(ctx, target_stream, data->buffer, data->len, sub);
+	// Skip first 2 bytes (same as original dvbsub_decode path in general_loop.c)
+	return route_dvb_stream_to_decoder(ctx, target_stream, data->buffer + 2, data->len - 2, sub);
 }
 
 int route_dvb_stream_to_decoder(struct lib_ccx_ctx *ctx, struct ccx_stream_metadata *stream,

src/rust/src/parser.rs

@@ -1567,7 +1567,7 @@ impl OptionsExt for Options {
                 );
             }
 
-            if self.demux_cfg.nb_ts_cappid > 0 {
+            if !self.demux_cfg.ts_cappids.is_empty() {
                 fatal!(
                     cause = ExitCause::IncompatibleParameters;
                     "Error: --split-dvb-subs cannot be used with manual PID selection (-pn).\n"