Fix #128933: Dyntopo density brush prints constant console errors

The brush does not use the value calculated from brush_strength, this
commit silences the assert by just handling the case statement for this
brush type with a static value of 0.0f.

Pull Request: https://projects.blender.org/blender/blender/pulls/128936

source/blender/editors/sculpt_paint/sculpt.cc

@@ -2204,6 +2204,10 @@ static float brush_strength(const Sculpt &sd,
     case SCULPT_BRUSH_TYPE_POSE:
     case SCULPT_BRUSH_TYPE_BOUNDARY:
       return root_alpha * feather;
+    case SCULPT_BRUSH_TYPE_SIMPLIFY:
+      /* The Dyntopo Density brush does not use a normal brush workflow to calculate the effect,
+       * and this strength value is unused. */
+      return 0.0f;
   }
   BLI_assert_unreachable();
   return 0.0f;