fix problem in initializing the custom_log_callbacks struct

it was an ordering problem

example/example.cpp

@@ -143,10 +143,10 @@ void callback_example()
 {
     // Define the callbacks
     spdlog::custom_log_callbacks callbacks;
-    callbacks.on_log_formatted = [](std::string str){
+    callbacks.on_log_formatted = [](std::string /*str*/){
         // do what you need to do with str
     };
-    callbacks.on_log = [](spdlog::details::log_msg msg){
+    callbacks.on_log = [](spdlog::details::log_msg /*msg*/){
         // do what you need to do with msg
     };
     

include/spdlog/sinks/callback_sink.h

@@ -15,14 +15,13 @@ namespace spdlog {
 // callbacks struct
 struct custom_log_callbacks
 {
-
     custom_log_callbacks()
         : on_log(nullptr)
         , on_log_formatted(nullptr)
     {}
 
-    std::function<void(const std::string &mag_str)> on_log_formatted;
     std::function<void(const details::log_msg &msg)> on_log;
+    std::function<void(const std::string &mag_str)> on_log_formatted;
 };
 
 namespace sinks {