🔧 Better BABYSTEP_MULTIPLICATOR_Z sanity-checks (#27471)

Author: ellensp

Marlin/src/inc/SanityCheck.h

@@ -500,10 +500,12 @@ static_assert(COUNT(arm) == LOGICAL_AXES, "AXIS_RELATIVE_MODES must contain " _L
   #elif ENABLED(BABYSTEP_XY) && !defined(BABYSTEP_MULTIPLICATOR_XY)
     #error "BABYSTEP_XY requires BABYSTEP_MULTIPLICATOR_XY."
   #elif ENABLED(BABYSTEP_MILLIMETER_UNITS)
-    static_assert(BABYSTEP_MULTIPLICATOR_Z <= 0.1f, "BABYSTEP_MULTIPLICATOR_Z must be less or equal to 0.1mm.");
+    static_assert(BABYSTEP_MULTIPLICATOR_Z <= 0.1f, "BABYSTEP_MULTIPLICATOR_Z with BABYSTEP_MILLIMETER_UNITS must be less or equal to 0.1mm.");
     #if ENABLED(BABYSTEP_XY)
       static_assert(BABYSTEP_MULTIPLICATOR_XY <= 0.25f, "BABYSTEP_MULTIPLICATOR_XY must be less than or equal to 0.25mm.");
     #endif
+  #else
+    static_assert(BABYSTEP_MULTIPLICATOR_Z && BABYSTEP_MULTIPLICATOR_Z == int(BABYSTEP_MULTIPLICATOR_Z), "BABYSTEP_MULTIPLICATOR_Z must be a non-zero integer.");
   #endif
 #endif