Micro optimize: don't init log_msg.msg_id on construction. It will be set anyway later

include/spdlog/details/log_msg.h

@@ -39,7 +39,7 @@ struct log_msg
     log_clock::time_point time;
     size_t thread_id;
     fmt::memory_buffer raw;
-    size_t msg_id{0};
+    size_t msg_id;
 
     // info about wrapping the formatted text with color (updated by pattern_formatter).
     mutable size_t color_range_start{0};

include/spdlog/details/pattern_formatter.h

@@ -714,11 +714,11 @@ private:
         case ('P'):
             formatters_.push_back(details::make_unique<details::pid_formatter>());
             break;
-
+#ifdef SPDLOG_ENABLE_MESSAGE_COUNTER
         case ('i'):
             formatters_.push_back(details::make_unique<details::i_formatter>());
             break;
-
+#endif
         case ('^'):
             formatters_.push_back(details::make_unique<details::color_start_formatter>());
             break;