🐛 Fix LCD contrast/brightness init (#23567)

Co-authored-by: Scott Lahteine <thinkyhead@users.noreply.github.com>

Marlin/src/lcd/marlinui.cpp

@@ -96,8 +96,7 @@ constexpr uint8_t epps = ENCODER_PULSES_PER_STEP;
 #endif
 
 #if HAS_LCD_CONTRAST
-  uint8_t MarlinUI::contrast; // Initialized by settings.load()
-
+  uint8_t MarlinUI::contrast = LCD_CONTRAST_DEFAULT; // Initialized by settings.load()
   void MarlinUI::set_contrast(const uint8_t value) {
     contrast = constrain(value, LCD_CONTRAST_MIN, LCD_CONTRAST_MAX);
     _set_contrast();