fix: crash when reading from stdin with no data

Two bugs: (1) general_loop.c dereferences NULL dec_ctx in the
live_stream progress code when no data was processed. (2) Rust
switch_to_next_file calls demux_ctx.open() for stdin, triggering
null pointer dereference via ptr::null().

Fix: add NULL check for dec_ctx in general_loop.c, and return
early from switch_to_next_file for stdin/network/tcp sources
instead of calling demux_ctx.open().

Author: Dhanush Varma

src/lib_ccx/general_loop.c

@@ -1507,7 +1507,7 @@ int general_loop(struct lib_ccx_ctx *ctx)
 			if (!data_node)
 				continue;
 		}
-		if (ctx->live_stream)
+		if (ctx->live_stream && dec_ctx)
 		{
 			LLONG t = get_fts(dec_ctx->timing, dec_ctx->current_field);
 			if (!t && ctx->demux_ctx->global_timestamp_inited)
@@ -1574,7 +1574,8 @@ int general_loop(struct lib_ccx_ctx *ctx)
 		}
 
 		// void segment_output_file(struct lib_ccx_ctx *ctx, struct lib_cc_decode *dec_ctx);
-		segment_output_file(ctx, dec_ctx);
+		if (dec_ctx)
+			segment_output_file(ctx, dec_ctx);
 
 		if (ccx_options.send_to_srv)
 			net_check_conn();

src/rust/src/file_functions/file.rs

@@ -161,15 +161,11 @@ pub unsafe fn switch_to_next_file(
     }
 
     // 2. Handle special input sources
-    #[allow(deref_nullptr)]
     match ccx_options.input_source {
         DataSource::Stdin | DataSource::Network | DataSource::Tcp => {
-            demux_ctx.open(*ptr::null(), ccx_options);
-            return match ret {
-                r if r < 0 => 0,
-                r if r > 0 => r,
-                _ => 1,
-            };
+            // For stdin/network/tcp, the fd is set up in demux_ctx.open()
+            // called from the main loop. Here we just need to signal success.
+            return 1;
         }
         _ => {}
     }