Set pid_tuning_finished globally to true

Use pid_tuning_finished as a flag to prevent automatic PID management.
As a result, set the default start-up state to true and adjust the
dependent code accordingly.

Firmware/temperature.cpp

@@ -85,7 +85,7 @@ float current_temperature_bed = 0.0;
 #ifdef PIDTEMP
   float _Kp, _Ki, _Kd;
   int pid_cycle, pid_number_of_cycles;
-  bool pid_tuning_finished = false;
+  bool pid_tuning_finished = true;
 #endif //PIDTEMP
   
 unsigned char soft_pwm_bed;

Firmware/ultralcd.cpp

@@ -1018,6 +1018,7 @@ void lcd_commands()
 			lcd_commands_step = 3;
 		}
 		if (lcd_commands_step == 3 && !blocks_queued()) { //PID calibration
+			pid_tuning_finished = false; // ensure we don't move to the next step early
 			sprintf_P(cmd1, PSTR("M303 E0 S%3u"), pid_temp);
 			// setting the correct target temperature (for visualization) is done in PID_autotune
 			enquecommand(cmd1);
@@ -1025,7 +1026,6 @@ void lcd_commands()
 			lcd_commands_step = 2;
 		}
 		if (lcd_commands_step == 2 && pid_tuning_finished) { //saving to eeprom
-			pid_tuning_finished = false;
 			custom_message_state = 0;
 			lcd_setstatuspgm(_i("PID cal. finished"));////MSG_PID_FINISHED c=20
 			setAllTargetHotends(0);  // reset all hotends temperature including the number displayed on the main screen