Only show custom bootscreen once

Marlin/src/lcd/ultralcd_impl_DOGM.h

@@ -278,6 +278,8 @@ void lcd_printPGM_utf(const char *str, uint8_t n=LCD_WIDTH) {
 
 #if ENABLED(SHOW_BOOTSCREEN)
 
+  bool show_bootscreen = true;
+
   #if ENABLED(SHOW_CUSTOM_BOOTSCREEN)
 
     void lcd_custom_bootscreen() {
@@ -294,8 +296,6 @@ void lcd_printPGM_utf(const char *str, uint8_t n=LCD_WIDTH) {
 
   void lcd_bootscreen() {
 
-    static bool show_bootscreen = true;
-
     if (show_bootscreen) {
       show_bootscreen = false;
 
@@ -353,11 +353,13 @@ static void lcd_implementation_init() {
   #endif
 
   #if ENABLED(SHOW_BOOTSCREEN)
+    if (show_bootscreen) {
       #if ENABLED(SHOW_CUSTOM_BOOTSCREEN)
         lcd_custom_bootscreen();
       #else
         lcd_bootscreen();
       #endif
+    }
   #endif
 }