Set seen_pointer before calling code_value

Marlin/Marlin_main.cpp

@@ -5220,6 +5220,7 @@ void process_next_command() {
   while (*current_command_args == ' ') ++current_command_args;
 
   // Interpret the code int
+  seen_pointer = current_command + 1;
   codenum = code_value_short();
 
   // Handle a known G, M, or T