Allowable range now includes default value

Marlin/Configuration.h

 #define CUSTOM_M_CODES
 #ifdef CUSTOM_M_CODES
   #define CUSTOM_M_CODE_SET_Z_PROBE_OFFSET 851
-  #define Z_PROBE_OFFSET_RANGE_MIN -2
-  #define Z_PROBE_OFFSET_RANGE_MAX 0
+  #define Z_PROBE_OFFSET_RANGE_MIN -15
+  #define Z_PROBE_OFFSET_RANGE_MAX -5
 #endif