Fix partial redraw during filament autoload

If the printer was already being pre-heated but didn't reach the target
temperature yet and a new filament is being inserted, the LCD used to
display a "Preheating to load" message to block the loading until the
extruder is hot.

This message is currently missing, and the ">Cancel" option doesn't
display immediately either, depending on the extruder height.

This PR fixes this behavior, which was broken during an earlier update.

We now force-update LCD updates during the first (and _only_) time the
screen is setup, and push all messages _before_ the carriage is
eventually raised, so that ">Cancel" is shown immediately as well.

Firmware/ultralcd.cpp

@@ -2201,15 +2201,16 @@ void mFilamentItem(uint16_t nTemp, uint16_t nTempBed)
     }
     else
     {
-        lcd_set_cursor(0, 0);
-        lcdui_print_temp(LCD_STR_THERMOMETER[0], (int) degHotend(0), (int) degTargetHotend(0));
-
         if (!bFilamentWaitingFlag)
         {
             // First run after the filament preheat selection:
             // setup the fixed LCD parts and raise Z as we wait
             bFilamentWaitingFlag = true;
 
+            lcd_clear();
+            lcd_draw_update = 1;
+            lcd_puts_at_P(0, 3, _i(">Cancel")); ////MSG_ c=20 r=1
+
             lcd_set_cursor(0, 1);
             switch (eFilamentAction)
             {
@@ -2236,9 +2237,11 @@ void mFilamentItem(uint16_t nTemp, uint16_t nTempBed)
                 // handled earlier
                 break;
             }
-            lcd_puts_at_P(0, 3, _i(">Cancel"));                   ////MSG_ c=20 r=1
         }
 
+        lcd_set_cursor(0, 0);
+        lcdui_print_temp(LCD_STR_THERMOMETER[0], (int) degHotend(0), (int) degTargetHotend(0));
+
         if (lcd_clicked())
         {
             bFilamentWaitingFlag = false;