Activate LiquidTWI2 device detection and space-pad LCD status line.

Marlin/Marlin_main.cpp

           lcd_update();
         }
       }else{
+          if (!lcd_detected())
+            break;
         while(!lcd_clicked()){
           manage_heater();
           manage_inactivity();

Marlin/ultralcd.cpp

     if (lcd_status_message_level > 0)
         return;
     strncpy(lcd_status_message, message, LCD_WIDTH);
+
+    size_t i = strlen(lcd_status_message);
+    memset(lcd_status_message + i, ' ', LCD_WIDTH - i);
+    lcd_status_message[LCD_WIDTH] = '\0';
+
     lcdDrawUpdate = 2;
 }
 void lcd_setstatuspgm(const char* message)
     if (lcd_status_message_level > 0)
         return;
     strncpy_P(lcd_status_message, message, LCD_WIDTH);
+
+    size_t i = strlen(lcd_status_message);
+    memset(lcd_status_message + i, ' ', LCD_WIDTH - i);
+    lcd_status_message[LCD_WIDTH] = '\0';
+
     lcdDrawUpdate = 2;
 }
 void lcd_setalertstatuspgm(const char* message)
     lastEncoderBits = enc;
 }
 
+bool lcd_detected(void)
+{
+#if (defined(LCD_I2C_TYPE_MCP23017) || defined(LCD_I2C_TYPE_MCP23008)) && defined(DETECT_DEVICE)
+  return lcd.LcdDetected() == 1;
+#else
+  return true;
+#endif
+}
+
 void lcd_buzz(long duration, uint16_t freq)
 {
 #ifdef LCD_USE_I2C_BUZZER

Marlin/ultralcd.h

   void lcd_setstatuspgm(const char* message);
   void lcd_setalertstatuspgm(const char* message);
   void lcd_reset_alert_level();
+  bool lcd_detected(void);
 
 #ifdef DOGLCD
   extern int lcd_contrast;
   FORCE_INLINE void lcd_buttons_update() {}
   FORCE_INLINE void lcd_reset_alert_level() {}
   FORCE_INLINE void lcd_buzz(long duration,uint16_t freq) {}
+  FORCE_INLINE bool lcd_detected(void) { return true; }
 
   #define LCD_MESSAGEPGM(x) 
   #define LCD_ALERTMESSAGEPGM(x) 

Marlin/ultralcd_implementation_hitachi_HD44780.h

   #include <Wire.h>
   #include <LiquidTWI2.h>
   #define LCD_CLASS LiquidTWI2
-  LCD_CLASS lcd(LCD_I2C_ADDRESS);
+  #if defined(DETECT_DEVICE)
+     LCD_CLASS lcd(LCD_I2C_ADDRESS, 1);
+  #else
+     LCD_CLASS lcd(LCD_I2C_ADDRESS);
+  #endif
   
 #elif defined(LCD_I2C_TYPE_MCP23008)
   #include <Wire.h>
   #include <LiquidTWI2.h>
   #define LCD_CLASS LiquidTWI2
-  LCD_CLASS lcd(LCD_I2C_ADDRESS);  
+  #if defined(DETECT_DEVICE)
+     LCD_CLASS lcd(LCD_I2C_ADDRESS, 1);
+  #else
+     LCD_CLASS lcd(LCD_I2C_ADDRESS);
+  #endif
 
 #elif defined(LCD_I2C_TYPE_PCA8574)
     #include <LiquidCrystal_I2C.h>