Fix destination unit creation in inverse

Author: mpusz

src/core/include/mp-units/math.h

@@ -413,13 +413,16 @@ template<Unit auto To, auto R, typename Rep>
   }
 {
 #if MP_UNITS_API_NATURAL_UNITS
-  if constexpr (!MP_UNITS_ASSOCIATED_UNIT<MP_UNITS_REMOVE_CONST(decltype(To))>)
-    return (representation_values<Rep>::one() * one).force_in(To * get_unit(R)) / q;
+  if constexpr (!MP_UNITS_ASSOCIATED_UNIT<MP_UNITS_REMOVE_CONST(decltype(To))>) {
+    constexpr Unit auto unit = To * quantity<R, Rep>::unit;
+    return (representation_values<Rep>::one() * one).force_in(unit) / q;
+  }
   else
 #endif
   {
     constexpr QuantitySpec auto qs = get_quantity_spec(To) * quantity<R, Rep>::quantity_spec;
-    return qs(representation_values<Rep>::one() * one).force_in(To * get_unit(R)) / q;
+    constexpr Unit auto unit = To * quantity<R, Rep>::unit;
+    return qs(representation_values<Rep>::one() * one).force_in(unit) / q;
   }
 }