Fix minor bugs discovered during alpha test

pkg/expression/eval.go

@@ -24,6 +24,9 @@ func Eval[T any](
 	}
 
 	value := buf.String()
+	if value == "" {
+		return result, nil
+	}
 	_, err = fmt.Sscanf(value, "%v", &result)
 	if err != nil {
 		return result, fmt.Errorf("unable to scan value '%v' into %T: %w", value, result, err)

pkg/streamcontrol/youtube/youtube.go

@@ -635,6 +635,9 @@ func (yt *YouTube) StartStream(
 		templateBroadcastIDs,
 		customArgs,
 	)
+	if len(templateBroadcastIDs) == 0 {
+		return fmt.Errorf("no template stream is selected")
+	}
 
 	templateBroadcastIDMap := map[string]struct{}{}
 	for _, broadcastID := range templateBroadcastIDs {

pkg/streampanel/panel.go

@@ -3532,6 +3532,10 @@ func (p *Panel) profileWindow(
 					youtubeProfile.Tags = sanitizeTags(getYoutubeTags())
 				}
 				profile.PerPlatform[youtube.ID] = youtubeProfile
+				if len(youtubeProfile.TemplateBroadcastIDs) == 0 {
+					p.DisplayError(fmt.Errorf("no youtube template stream is selected"))
+					return
+				}
 			}
 			err := commitFn(ctx, profile)
 			if err != nil {