Fixed unspecified monitor streaming the whole X

sunshine/config.cpp

@@ -105,7 +105,8 @@ video_t video {
 
   {}, // encoder
   {}, // adapter_name
-  {}  // output_name
+  {},  // output_name
+  -1
 };
 
 audio_t audio {};
@@ -371,6 +372,8 @@ void apply_config(std::unordered_map<std::string, std::string> &&vars) {
 
   string_f(vars, "audio_sink", audio.sink);
 
+  int_between_f(vars, "linux_monitor_id", video.linux_monitor_id, { 0, 32 });
+
   string_restricted_f(vars, "origin_pin_allowed", nvhttp.origin_pin_allowed, {
     "pc"sv, "lan"sv, "wan"sv
   });