Always define MIN_Z_HEIGHT_FOR_HOMING even if 0

Always define MIN_Z_HEIGHT_FOR_HOMING even if 0
Always make a potential rise to `home_offset[Z_AXIS]` possible in G28.
Get rid of some very ugly constructs in MBL (ultralcd.cpp).

Marlin/Marlin_main.cpp

@@ -2892,7 +2892,7 @@ inline void gcode_G28() {
         #endif
       }
 
-    #elif defined(MIN_Z_HEIGHT_FOR_HOMING) && MIN_Z_HEIGHT_FOR_HOMING > 0
+    #else
 
       if (home_all_axis || homeX || homeY) {
         // Raise Z before homing any other axes and z is not already high enough (never lower z)
@@ -2913,7 +2913,7 @@ inline void gcode_G28() {
         }
       }
 
-    #endif // MIN_Z_HEIGHT_FOR_HOMING
+    #endif
 
     #if ENABLED(QUICK_HOME)