add (void)0 when logging is disabled

include/spdlog/spdlog.h

@@ -173,16 +173,15 @@ void drop_all();
 #    define SPDLOG_TRACE(logger, ...) logger->trace("[ " __FILE__ ":" SPDLOG_STR_HELPER(__LINE__) " ] " __VA_ARGS__)
 #  endif
 #else
-#define SPDLOG_TRACE(logger, ...)
+#  define SPDLOG_TRACE(logger, ...) (void)0
 #endif
 
 #ifdef SPDLOG_DEBUG_ON
 #  define SPDLOG_DEBUG(logger, ...) logger->debug(__VA_ARGS__)
 #else
-#define SPDLOG_DEBUG(logger, ...)
+#  define SPDLOG_DEBUG(logger, ...) (void)0
 #endif
 
 }
 
-
 #include "details/spdlog_impl.h"