Only look for "N" line number as first parameter

Marlin/Marlin_main.cpp

@@ -834,8 +834,10 @@ void get_command() {
         fromsd[cmd_queue_index_w] = false;
       #endif
 
-      char *npos = strchr(command, 'N');
+      while (*command == ' ') command++; // skip any leading spaces
-      char *apos = strchr(command, '*');
+      char* npos = (*command == 'N') ? command : NULL; // Require the N parameter to start the line
+      char* apos = strchr(command, '*');
+
       if (npos) {
 
         boolean M110 = strstr_P(command, PSTR("M110")) != NULL;