M29 match logic was reversed (#13013)

* M29 logic was reversed 

If in card-saving mode generate errors line errors for anything that's *NOT* "M29 ?"

* Update queue.cpp

* Update queue.cpp

Marlin/src/gcode/queue.cpp

@@ -536,6 +536,10 @@ void gcode_line_error(PGM_P err, uint8_t port) {
 
 #endif // FAST_FILE_TRANSFER
 
+FORCE_INLINE bool is_M29(const char * const cmd) {
+  return cmd[0] == 'M' && cmd[1] == '2' && cmd[2] == '9' && !WITHIN(cmd[3], '0', '9');
+}
+
 /**
  * Get all commands waiting on the serial port and queue them.
  * Exit when the buffer is full or when no more characters are
@@ -631,7 +635,8 @@ inline void get_serial_commands() {
           gcode_LastN = gcode_N;
         }
         #if ENABLED(SDSUPPORT)
-          else if (card.flag.saving && command[0] == 'M' && command[1] == '2' && command[2] == '9' && (command[3] == '\0' || command[3] == ' '))
+          // Pronterface "M29" and "M29 " has no line number 
+          else if (card.flag.saving && !is_M29(command))
             return gcode_line_error(PSTR(MSG_ERR_NO_CHECKSUM), i);
         #endif
 
@@ -840,7 +845,7 @@ void advance_command_queue() {
 
     if (card.flag.saving) {
       char* command = command_queue[cmd_queue_index_r];
-      if (command[0] == 'M' && command[1] == '2' && command[2] == '9' && (command[3] == '\0' || command[3] == ' ')) {
+      if (is_M29(command)) {
         // M29 closes the file
         card.closefile();
         SERIAL_ECHOLNPGM(MSG_FILE_SAVED);