Fix for thePR #5267 (Introduce a +1234.56 format for over 999 steps/mm)

・Fix memory leak

Marlin/utility.cpp

 
 #if ENABLED(ULTRA_LCD)
 
-  char conv[8];
+  char conv[9];
 
   #define DIGIT(n) ('0' + (n))
   #define DIGIMOD(n, f) DIGIT((n)/(f) % 10)