fix: use log.file=eventlog as default value, if running as windows service (#1771)

Signed-off-by: Jan-Otto Kröpke <mail@jkroepke.de>

internal/log/logger.go

@@ -34,6 +34,10 @@ type AllowedFile struct {
 }
 
 func (f *AllowedFile) String() string {
+	if f == nil {
+		return ""
+	}
+
 	return f.s
 }