🩹 Init fan speed at boot (#23181)

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

Marlin/src/module/planner.cpp

@@ -1309,7 +1309,7 @@ void Planner::check_axes_activity() {
   #endif
 
   #if HAS_TAIL_FAN_SPEED
-    static uint8_t tail_fan_speed[FAN_COUNT];
+    static uint8_t tail_fan_speed[FAN_COUNT] = ARRAY_N_1(FAN_COUNT, 255);
     bool fans_need_update = false;
   #endif