Correct mesh size calculations

Marlin/src/inc/Conditionals_post.h

     #if ENABLED(AUTO_BED_LEVELING_UBL)
       #define _MESH_MIN_X (max(X_MIN_BED + MESH_INSET, X_MIN_POS))  // UBL is careful not to probe off the bed.  It does not
       #define _MESH_MIN_Y (max(Y_MIN_BED + MESH_INSET, Y_MIN_POS))  // need *_PROBE_OFFSET_FROM_EXTRUDER in the mesh dimensions
+      #define _MESH_MAX_X (min(X_MAX_BED - (MESH_INSET), X_MAX_POS))
+      #define _MESH_MAX_Y (min(Y_MAX_BED - (MESH_INSET), Y_MAX_POS))
     #else
       #define _MESH_MIN_X (max(X_MIN_BED + MESH_INSET, X_MIN_POS + X_PROBE_OFFSET_FROM_EXTRUDER))
       #define _MESH_MIN_Y (max(Y_MIN_BED + MESH_INSET, Y_MIN_POS + Y_PROBE_OFFSET_FROM_EXTRUDER))
+      #define _MESH_MAX_X (min(X_MAX_BED - (MESH_INSET), X_MAX_POS + X_PROBE_OFFSET_FROM_EXTRUDER))
+      #define _MESH_MAX_Y (min(Y_MAX_BED - (MESH_INSET), Y_MAX_POS + Y_PROBE_OFFSET_FROM_EXTRUDER))
     #endif
   #endif
   /**